Exhibit 4.1

                INTERSTATE POWER AND LIGHT COMPANY


                       OFFICER'S CERTIFICATE


                    Dated as of August 2, 2004


                      ______________________


               Reopening a Series of Debt Securities


                 6.30% Senior Debentures due 2034


                      ______________________


                     Pursuant to the Indenture
                    Dated as of August 20, 2003







                       OFFICER'S CERTIFICATE

           The  undersigned,  the Vice  President  and Treasurer of
Interstate  Power  and  Light  Company,  an Iowa  corporation  (the
"Company"),  hereby certifies as provided below pursuant to Section
301  of  the   Indenture,   dated  as  of  August  20,   2003  (the
"Indenture"),  between the Company and J.P.  Morgan Trust  Company,
National  Association,   successor,  as  Trustee  (the  "Trustee").
This  Officer's  Certificate,  dated August 2, 2004,  is delivered,
pursuant to authority  granted to the  undersigned  by  resolutions
adopted  January  28,  2004  by  the  Board  of  Directors  of  the
Company,  for the purpose of  reopening  pursuant to Section 301 of
the Indenture a series of  securities  under the  Indenture,  which
series was  previously  created,  whose terms were  previously  set
forth and to whose form were previously  established,  in each case
pursuant  to an  Officer's  Certificate,  dated  as of May 3,  2004
(the "May  Certificate"),  in  accordance  with  Section 201 of the
Indenture.  Capitalized  terms not  otherwise  defined  herein  are
used as defined in the Indenture.

        1.    The Board of  Directors  of the  Company has  authorized
the creation by the Company of one or more series of  Securities
under the  Indenture  through  one or  more  Officer's  Certificates
and pursuant  to  such   authorization   and  in  accordance  with  the
Indenture  this  Officer's  Certificate  is being  delivered to the
Trustee  to reopen  the  series of  Securities  created  by the May
Certificate,  increasing  the  aggregate  principal  amount of such
Securities by $25,000,000.

        2.    As  established  by the May  Certificate,  the  title
of the series of Securities  shall be "6.30% Senior  Debentures  due
2034"(herein called the "Debentures").

        3.    The aggregate  principal  amount of the Debentures
which may be  authenticated  and delivered  under the Indenture shall
be U.S.$125,000,000   ($25,000,000  of  which  may  be  authenticated
and delivered  pursuant to this Officer's  Certificate and $100,000,000
of  which  was  authenticated  and  delivered  pursuant  to the May
Certificate),  except for  Debentures  authenticated  and delivered
upon  registration  of transfer of, or in exchange  for, or in lieu
of, other  Debentures  as provided in Sections  304,  305, 306, 406
or 1206 of the Indenture.  Notwithstanding  the foregoing  limit on
the aggregate  principal  amount of the Debentures,  the Debentures
may be reopened in accordance with Section 301 of the Indenture.

        4.    The Debentures  shall be issuable in  denominations of
$1,000 and any integral multiple thereof.

        5.    Subject  to  earlier   redemption,   the   principal  of
the Debentures shall be payable in U.S. dollars on May 1, 2034.

        6.    The  Debentures  shall bear interest at the rate of 6.30%
per annum;  such  interest  shall  accrue from May 6, 2004 (or from and
including the most recent  interest  payment date to which interest
on the  Debentures  has been paid or provided  for);  the  Interest
Payment  Dates on which such  interest  shall be  payable  shall be
May 1 and  November 1 in each year,  commencing  November  1, 2004;
the Regular Record Dates for the  determination  of Holders to whom
interest is payable  shall be (1) the Business  Day next  preceding
each  Interest   Payment  Date,   if  the   Debentures   remain  in
book-entry  only form, or (2) on the fifteenth  calendar day before





each  Interest  Payment  Date,  if the  Debentures do not remain in
book-entry  only  form.   Interest  on  the  Debentures   shall  be
payable in U.S. dollars.

        7.    Pursuant to the Indenture,  the Trustee has been appointed
as the Security  Registrar for the  Debentures.  The Trustee is hereby
further  appointed as the initial  Paying Agent and transfer  agent
of  the   Debentures.   The   principal  of  and  interest  on  the
Debentures  shall be payable  at the  office of the  Paying  Agent,
which shall  initially be located in the Borough of Manhattan,  The
City of New York.

        8.    The  Debentures  shall be  redeemable  at the  option
of the Company  at any  time in  whole  or from  time to time in part at a
Redemption  Price  equal to the sum of  (a)100%  of the  principal
amount  of the  Debentures  being  redeemed,  (b)accrued  interest
thereon to the Redemption Date, and (c)the  Make-Whole  Amount, if
any,  with  respect to such  Debentures;  provided,  however,  that
installments  of interest on Debentures due on an Interest  Payment
Date  which  occurs  on or  before  any  Redemption  Date  shall be
payable  to the  Holders  of such  Debentures  who were  registered
Holders  as  of  the  close  of   business   on  the  Record   Date
immediately preceding such Interest Payment Date.

        9.    The  terms  defined  below  shall,  for all  purposes
of the Debentures  under the  Indenture  and this  Officer's  Certificate,
have the meanings  specified,  unless the context clearly otherwise
requires or unless otherwise indicated:

           "Make-Whole   Amount"  means,  in  connection  with  any
optional  redemption,  the  excess,  if any,  of (i) the  aggregate
present  value as of the date of such  redemption of each dollar of
principal  being redeemed and the amount of interest,  exclusive of
interest  accrued  to the  Redemption  Date,  that  would have been
payable in respect of each such dollar if such  redemption  had not
been made,  determined  by  discounting,  on a  semi-annual  basis,
such   principal  and  interest  at  the   Reinvestment   Rate,  as
determined  on the  third  Business  Day  preceding  the date  such
notice of redemption is given,  from the respective  dates on which
such  principal  and  interest  would  have  been  payable  if such
redemption  had not been made, to the  Redemption  Date,  over (ii)
the aggregate  principal  amount of the Debentures  being redeemed.
The  Make-Whole  Amount shall be  calculated by the Company and set
forth in a certificate  of an Authorized  Officer  delivered to the
Trustee,  and  the  Trustee  shall  be  entitled  to  rely  on said
certificate.

           "Reinvestment  Rate" means .20% plus the arithmetic mean
of the yields under the  headings  "Week  Ending"  published in the
most  recent  Statistical   Release  under  the  caption  "Treasury
Constant  Maturities"  for the  maturity,  rounded  to the  nearest
month,  corresponding to the remaining life to maturity,  as of the
payment  date  of the  principal  amount  of the  Debentures  being
redeemed.  If no maturity  exactly  corresponds  to such  maturity,
yields   for   the   two   published    maturities   most   closely
corresponding  to such  maturity  shall be  calculated  pursuant to
the  immediately  preceding  sentence  and  the  Reinvestment  Rate
shall  be  interpolated  or  extrapolated  from  such  yields  on a
straight-line  basis,  rounding in each of such relevant periods to
the nearest  month.  For purposes of calculating  the  Reinvestment
Rate, the most recent  Statistical  Release  published prior to the
date of  determination  of the Make-Whole  Amount shall be used. If




the  format or  content  of the  Statistical  Release  changes in a
manner that  precludes  determination  of the Treasury yield in the
above  manner,  then the Treasury  yield shall be determined in the
manner  that  most  closely   approximates  the  above  manner,  as
reasonably determined by the Company.

           "Statistical  Release"  means  the  statistical  release
designated  "H.15(519)"  or  any  successor  publication  which  is
published  weekly by the Federal  Reserve  System and which reports
yields on  actively  traded  United  States  government  securities
adjusted to constant  maturities,  or, if such statistical  release
is not  published at the time of any required  determination  under
the Indenture,  then such other  reasonably  comparable index which
shall be designated by the Company.

        10.   The  Debentures  shall not be subject to any sinking fund
and shall  not  be  repurchasable  or  redeemable  at the  option  of a
Holder.

        11.   The   Debentures   shall  not  be   convertible   into
other securities  of  the  Company  or  exchangeable  for  securities  of
another issuer.

        12.   Satisfaction   and   discharge   under  Section  701  of
the Indenture  shall  be  applicable  to  the   Debentures;   provided,
however,  that prior to any such  satisfaction  and discharge,  the
Company  shall have  delivered to the Trustee an Opinion of Counsel
stating  that  (a) the  Company  has  received  from  the  Internal
Revenue  Service a letter  ruling,  or there has been  published by
the Internal  Revenue  Service a revenue  ruling,  or (b) since the
date of execution of this Officer's  Certificate,  there has been a
change in the  applicable  Federal  income tax law,  in either case
to the effect that,  and based  thereon such opinion  shall confirm
that,  the  Holders  of  such   Outstanding   Securities  will  not
recognize  income,  gain or loss for  Federal  income tax  purposes
as a  result  of  such  satisfaction  and  discharge  and  will  be
subject to  Federal  income  tax on the same  amounts,  in the same
manner  and at the same  times as would  have been the case if such
satisfaction and discharge had not occurred.

        13.   The  Debentures  shall  initially  be  issued in whole
in the form of one or more  permanent  global  Securities.  The Depository
Trust  Company  ("DTC"),  a clearing  agency  registered  under the
Securities  Exchange  Act of  1934,  as  amended,  shall  initially
serve as the  depositary  for such global  Security or  Securities.
For so long as DTC shall be the  depositary,  all Debentures  shall
be  registered  in its  name or in the name of a  nominee  thereof.
While  the   Debentures   are  evidenced  by  one  or  more  global
Securities,  the  depositary  or its  nominee,  as the case may be,
shall  be the  sole  Holder  thereof  for all  purposes  under  the
Indenture.  Neither  the  Company  nor the  Trustee  shall have any
responsibility  or obligation to the  depositary's  participants or
the  beneficial  owners  for whom  they act with  respect  to their
receipt  from the  depositary  of  payments  on the  Debentures  or
notices  given  under  the  Indenture.   The  global   Security  or
Securities  provided  for  hereunder  shall  bear  such  legend  or
legends as may be required from time to time by the depositary.

        14.   Except as herein  described,  Debentures in  definitive
form will not be issued.  Notwithstanding  the  foregoing,  in the
event the Company  decides to discontinue  the use of global  Securities,
any Event of Default has  occurred and is  continuing  or DTC is at




any  time   unwilling,   unable  or   ineligible   to  continue  as
depositary  and a  successor  depositary  is not  appointed  by the
Company  within  90  days,  the  Company  shall  issue   individual
Debentures  in   certificated   form  to  owners  of   "book-entry"
ownership  interests in exchange for the Debentures  held by DTC or
its nominee,  as the case may be. In such  instance,  an owner of a
"book-entry"  ownership  interest  will  be  entitled  to  physical
delivery  of  certificates   equal  in  principal  amount  to  such
"book-entry"  ownership  interest  and to  have  such  certificates
registered  in its name.  Individual  certificates  so issued  will
be issued in denominations of $1,000 or any multiple thereof.

        15.   Additional  terms  regarding the  Debentures are as set
forth in the form of the Debentures set forth below.

        16.   The form of the Debentures shall be substantially as follows:






      Unless  this   certificate  is  presented  by  an  authorized
representative  of  The  Depository  Trust  Company,   a  New  York
corporation  ("DTC"),  to the  Company  (as  defined  below) or its
agent for  registration of transfer,  exchange or payment,  and any
certificate  issued is  registered  in the name of Cede & Co. or in
such other name as is  requested  by an  authorized  representative
of DTC  (and any  payment  is made to Cede & Co.  or to such  other
entity as is requested  by an  authorized  representative  of DTC),
ANY  TRANSFER,  PLEDGE OR OTHER USE HEREOF  FOR VALUE OR  OTHERWISE
BY OR TO ANY PERSON IS WRONGFUL  inasmuch as the  registered  owner
hereof, Cede & Co., has an interest herein.

                INTERSTATE POWER AND LIGHT COMPANY

                 6.30% SENIOR DEBENTURES DUE 2034

No.                                                $_______________
                                              CUSIP No. 461070 AD 6

      INTERSTATE  POWER  AND  LIGHT  COMPANY,  a  corporation  duly
organized  and  existing  under  the  laws  of the  State  of  Iowa
(herein  called the  "Company,"  which term  includes any successor
Person  under the  Indenture  hereinafter  referred  to), for value
received,  hereby  promises  to pay to  Cede & Co.,  or  registered
assigns,    the   principal    sum   of    ________________________
($__________)  on May 1, 2034 and to pay interest on said principal
sum  from  May 6,  2004,  or from and  including  the  most  recent
interest  payment  date to which  interest  has  been  paid or duly
provided for,  semi-annually,  in arrears,  on May 1 and November 1
of  each  year  (each  such  date,  an  "Interest  Payment  Date"),
commencing  November 1,  2004 at the rate of 6.30%  per  annum  to,
but not including,  the date on which the principal  hereof is paid
or made available for payment.  The amount of interest  payable for
any period will be computed  on the basis of twelve  30-day  months
and a 360-day year. The interest so payable,  and  punctually  paid
or duly  provided  for,  on any  Interest  Payment  Date  will,  as
provided  in the  Indenture,  be paid to the  Person in whose  name
this Debenture (or one or more Predecessor  Securities,  as defined
in the  Indenture) is  registered at the close of business,  on the
Regular  Record  Date for  such  interest,  which  shall be (1) the
Business Day next  preceding  each such  Interest  Payment Date, if
the  Debentures  remain  in  book-entry  only  form,  or (2) on the
fifteenth  calendar day before each  interest  payment date, if the
Debentures  do  not  remain  in  book-entry  only  form.  Any  such
interest  installment  not so punctually  paid or duly provided for
shall  forthwith  cease to be payable to the  registered  Holder on
such  Regular  Record  Date and may either be paid to the Person in
whose name this Debenture (or one or more  Predecessor  Securities)
is  registered  at the close of business  on a Special  Record Date
for the  payment  of such  Defaulted  Interest  to be  fixed by the
Trustee,  notice  whereof  shall be given to Holders of  Debentures
not later than 10 days prior to such  Special  Record  Date,  or be
paid at any time in any other lawful manner not  inconsistent  with
the   requirements   of  any  securities   exchange  on  which  the
Debenture  may be listed,  or any  book-entry  system  which may be
applicable  to  this  Debenture  and  upon  such  notice  as may be
required  by such  exchange or system,  all as more fully  provided
in the Indenture.

      Payment of the  principal  of and  interest on any  Debenture
that is not a  global  Debenture  will be  made  at the  office  or
agency of the Company  maintained  for that  purpose in The City of
New York;  provided,  however,  that at the  option of the  Company
payment  of  interest  may be  made  (i)  by  check  mailed  to the
address  of the  Person  entitled  thereto  as such  address  shall
appear  in the  Security  Register  or  (ii) by  wire  transfer  in
immediately  available  funds at such place and to such  account as
may be  designated by the Person  entitled  thereto as specified in
the  Security  Register.  Payment of  principal  of and interest on
any global  Debenture  will be made to DTC or its  nominee,  as the
case may be, as the sole  registered  owner and the sole  Holder of
the  global   Debenture  for  all  purposes  under  the  Indenture.
Payment of the  principal  of and interest on this  Debenture  will
be made in such coin or  currency  of the United  States of America
as at the time of  payment is legal  tender  for  payment of public
and private debts.

      Additional  provisions of this Debenture are continued on the
two  pages  following  the  execution  and  authentication  of this
Debenture  and  such  provisions  have the same  effect  as  though
fully set forth in this place.

      Unless  the  certificate  of  authentication  hereon has been
executed by or on behalf of the Trustee by manual  signature,  this
Debenture   shall  not  be  entitled  to  any  benefit   under  the
Indenture or be valid or obligatory for any purpose.




      IN WITNESS  WHEREOF,  INTERSTATE  POWER AND LIGHT COMPANY has
caused this  instrument  to be duly  executed  under its  corporate
seal.


Dated: __________ __, 20__


                               INTERSTATE POWER AND LIGHT COMPANY



                               By:
                                 ---------------------------------
                                 Name
                                 Title

Attest:



- -------------------------
Authorized Officer



                     Trustee's Certificate of Authentication
                     ---------------------------------------

   This is one of the Debentures of the series designated herein
          referred to in the within-mentioned Indenture.

                               J.P. MORGAN TRUST COMPANY,  NATIONAL
                               ASSOCIATION,
                                    as Trustee



                               By:
                                  -------------------------------
                                  Authorized Officer






                INTERSTATE POWER AND LIGHT COMPANY
                 6.30% SENIOR DEBENTURES DUE 2034


      This  Debenture  is  one  of  a  duly  authorized   issue  of
Debentures  of  the  Company,   designated  as  its  "6.30%  Senior
Debentures   due  2034"  (herein  called  the  "Debentures"),   in
aggregate  principal  amount  of  $125,000,000,   issued  under  an
Indenture,   dated  as  of  August  20,  2003   (herein   call  the
"Indenture"),  between the Company and J.P.  Morgan Trust  Company,
National  Association,  successor,  as Trustee (the "Trustee"),  to
which  Indenture  and  the  Officer's  Certificates,  dated  May 3,
2004,  and August 2, 2004,  setting forth the terms and  conditions
of the  Debentures,  reference  is hereby made for a  statement  of
the  respective   rights,   limitations   of  rights,   duties  and
immunities  thereunder of the Trustee,  the Company and the Holders
of the  Debentures,  and of the terms upon which the Debenture are,
and are to be, authenticated and delivered.

      The  Company  may  redeem the  Debentures  at any time at the
Company's  option,  in  whole  or in part,  at a  redemption  price
equal to the sum of the  principal  amount  of the  Debentures  the
Company  redeems,  accrued interest on that principal amount to the
redemption  date  and the  Make-Whole  Amount  (as  defined  in the
Officer's Certificate), if any, with respect to those Debentures.

      If an Event of Default with respect to the  Debentures  shall
occur and be  continuing,  the principal of the  Debentures  may be
declared  due and  payable  in the  manner,  with  the  effect  and
subject to the conditions, provided in the Indenture.

      The  Indenture  contains   provisions  for  satisfaction  and
discharge  at  any  time  of  the  entire   indebtedness   of  this
Debenture  upon  compliance by the Company with certain  conditions
set forth in the Indenture.

      The Indenture contains provisions  permitting the Company and
the  Trustee,  with the  consent of the  Holders of not less than a
majority in  principal  amount of the  Outstanding  Debentures,  to
modify  the  Indenture  in a manner  affecting  the  rights  of the
Holders  of the  Debentures;  provided  that no  such  modification
may,  without  the  consent  of  the  Holder  of  each  Outstanding
Debenture,  (i) change the Stated  Maturity of, the  principal  of,
or any  installment  of  principal  of or  interest  on  (except as
provided  in  Section  312 of the  Indenture),  any  Debenture,  or
reduce  the  principal  amount  thereof  or the  rate  of  interest
thereon (or the amount of any  installment of interest  thereon) or
change the method of  calculating  such rate or reduce any  premium
payable  upon  the  redemption  thereof,  or  change  the  coin  or
currency  (or  other  property),  in which  the  Debentures  or any
premium or the  interest  thereon is  payable,  or impair the right
to  institute  suit for the  enforcement  of any such payment on or
after the  Stated  Maturity  of any  Debenture  or (ii)  reduce the
percentage  in principal  amount of the  Outstanding  Debentures of
any series or any  Tranche  thereof,  the consent of the Holders of
which is  required  for any  such  modification  of the  Indenture.
The  Indenture  also  contains  provisions  permitting  Holders  of
specified  percentages  in principal  amount of the  Debentures  at
the time  Outstanding,  on behalf of the Holders of all Debentures,
to waive  compliance by the Company with certain  provisions of the
Indenture and certain past  defaults  under the Indenture and their
consequences.  Any such  consent  or waiver  by the  Holder of this
Debenture  shall be  conclusive  and  binding  upon such Holder and
upon all future  Holders  of this  Debenture  and of any  Debenture
issued  upon the  registration  of  transfer  hereof or in exchange
herefor  or in  lieu  hereof,  whether  or  not  notation  of  such
consent or waiver is made upon this Debenture.

      No  reference  herein to the  Indenture  and no  provision of
this  Debenture  or of the  Indenture  shall  alter or  impair  the
obligation  of the Company,  which is absolute  and  unconditional,
to pay the  principal  of and  interest  on this  Debenture  at the
times,  place  and  rate,  and  in the  coin  or  currency,  herein
prescribed.

      As  provided  in  the   Indenture   and  subject  to  certain
limitations,  including,  if this Debenture is a global  Debenture,
the  limitations  set forth on the first page  hereof,  therein set
forth,  the  transfer  of  this  Debenture  is  registrable  in the
Security   Register,   upon   surrender  of  this   Debenture   for
registration  of  transfer  at the office or agency of the  Company
in  The  City  of  New  York  maintained  for  such  purpose,  duly
endorsed by, or  accompanied  by a written  instrument  of transfer
in form  satisfactory  to the  Company and the  Security  Registrar
duly   executed  by,  the  Holder   hereof  or  his  attorney  duly
authorized in writing,  and  thereupon one or more new  Debentures,
of authorized  denominations  and for the same aggregate  principal
amount,   will  be  issued   to  the   designated   transferee   or
transferees.   No  service  charge  shall  be  made  for  any  such
registration  of transfer or exchange,  but the Company may require
payment   of  a  sum   sufficient   to  cover   any  tax  or  other
governmental charge payable in connection therewith.

      Prior to due  presentment of this Debenture for  registration
of  transfer,  the  Company,  the  Trustee  and  any  agent  of the
Trustee  may treat  the  Person in whose  name  this  Debenture  is
registered  as the owner  hereof for all  purposes,  whether or not
this  Debenture be overdue,  and neither the  Company,  the Trustee
nor any such agent shall be affected by notice to the contrary.

      The Debentures  are issuable only in registered  form without
coupons  in  denominations  of  $1,000  and any  integral  multiple
thereof.




      All terms  used in this  Debenture  which are  defined in the
Indenture  shall  have  the  meanings   assigned  to  them  in  the
Indenture.

      THIS  DEBENTURE   SHALL  BE  GOVERNED  BY  AND  CONSTRUED  IN
ACCORDANCE  WITH THE LAWS OF THE STATE OF NEW YORK  WITHOUT  REGARD
TO CONFLICTS OF LAWS PRINCIPLES THEREOF.





           IN WITNESS WHEREOF,  the undersigned has set his hand as
of the day and year first above written.


                          INTERSTATE POWER AND LIGHT COMPANY


                               By:  /s/ Thomas L. Hanson
                                    -------------------------
                                    Thomas L. Hanson
                                    Vice President and Treasurer