Old Second Bancorp (OSBC) 8-K Other Events

Exhibit 99.1

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Forward-looking Statements and Non-GAAP Disclosures [LOGO]

In addition to historical information, this presentation contains forward-looking statements, which are subject to certain risks and uncertainties. Forward-looking statements include information concerning possible or assumed future results of Old Second’s operations.  Forward-looking statements generally include words such as believes, expects, anticipates and other similar expressions.

Stockholders should note that many factors could affect the future financial results of Old Second, causing those results to differ materially from those expressed in this presentation. These factors include operating, legal and regulatory risks; economic, political and competitive forces impacting our business; risk that our analysis of these risks and forces could be incorrect and/or that the strategies developed to address them could be unsuccessful; volatility in interest rates; and other risks and uncertainties which are summarized in our SEC filings.

Old Second undertakes no obligation to publicly revise or update these forward-looking statements to reflect events that arise after this presentation.

Statements in this presentation may also include adjusted non-GAAP financial measures governed by Regulation G. Generally, we believe that these measures and ratios provide users of our financial information a more accurate view of the performance of the interest-earning assets and interest-bearing liabilities and of our operating efficiency for comparative purposes with other financial holding companies. The reconciliation of each non-GAAP presentation is included herein.

Right sized banking.

Who We Are

•$2.3 billion financial holding company headquartered in Aurora, Illinois

•3 independently chartered community banks

•Trust & Investment Group with over $1 billion under management

•Mortgage company

•27 locations

•64 ATM locations

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Illinois’ Largest Cities

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(Excluding Chicago)

Illinois’ Fastest Growing Cities: Net Gain 1990-2000

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Illinois’ Fastest Growing Counties by %

7/1/01-7/1-02 (out of 102 counties)

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NE Illinois Planning Commission Population Forecasts

	2000	2030	Difference	% Change
DuPage Cty.	904,161	1,002,325	98,164	10.86	%
Kane Cty.	404,119	692,346	288,227	71.32	%
Aurora (excl. Kend.)	142,150	190,167	48,017	33.78	%
Batavia	23,866	31,402	7,536	31.58	%
Elgin	94,487	162,416	67,929	71.89	%
Geneva	19,515	25,480	5,965	30.57	%
North Aurora	10,585	20,694	10,109	95.50	%
St. Charles	27,896	36,671	8,775	31.46	%
South Elgin	16,100	27,567	11,467	71.22	%
Sugar Grove	3,909	62,742	58,833	1505.07	%

Old Second Kane County Market Leader

	1999		2000		2001		2002		2003		2004		2005
	% Mkt		% Mkt		% Mkt		% Mkt		% Mkt		% Mkt		% Mkt
O2	13.08	%	15.07	%	16.19	%	17.21	%	17.34	%	17.97	%	18.44	%
Harris	10.41	%	10.80	%	10.82	%	10.49	%	10.59	%	11.61	%	10.54	%
5/3	20.86	%	17.72	%	15.98	%	13.41	%	11.30	%	9.70	%	9.49	%
Chase	11.60	%	10.62	%	8.92	%	8.82	%	9.48	%	8.64	%	8.55	%
EFS	6.02	%	6.88	%	6.73	%	7.20	%	7.35	%	7.80	%	8.17	%
1st Am	4.50	%	5.35	%	5.52	%	5.00	%	4.81	%	4.37	%	4.14	%

Remaining 40 banks each have less than 4% share of Kane County market.

Old Second Kendall County Market Leader

	1999		2000		2001		2002		2003		2004		2005
	% Mkt		% Mkt		% Mkt		% Mkt		% Mkt		% Mkt		% Mkt
O2	21.38	%	24.40	%	25.67	%	28.53	%	30.21	%	32.39	%	33.46	%
OswgoC	15.05	%	10.11	%	15.66	%	16.38	%	15.93	%	15.49	%	14.27	%
Castle	13.10	%	12.54	%	12.42	%	12.79	%	13.38	%	13.77	%	14.36	%
Harris	5.00	%	5.98	%	5.47	%	12.15	%	11.57	%	9.89	%	8.79	%
Union	8.37	%	8.14	%	7.24	%	7.29	%	7.54	%	7.52	%	7.68	%
5/3	14.87	%	11.17	%	10.03	%	8.09	%	6.69	%	6.06	%	6.15	%

Remaining 8 banks each have less than 5% share of Kane County market.

Deposit Market Share

AURORA (KANE)

	# of	Deposits	Market
	offices	($000)	Share
Old Second	4	732,309	47.93	%
Fifth Third	4	223,071	14.60	%
Harris Aurora	4	137,351	8.99	%
Benchmark	1	121,812	7.97	%
West Suburban	3	92,276	6.04	%
National City	2	73,533	4.81	%
Banco Popular	2	64,671	4.23	%

YORKVILLE

	# of	Deposits	Market
	offices	(000s)	Share
OSB-Yorkville	2	232,065	61.42	%
Castle Bank	1	131,005	34.67	%
Union Bank	1	10,286	2.72	%
TCF Bank	1	2,238	0.59	%

ELBURN

OSB-Kane Cty.	1	119,815	74.14	%
American B&T	1	22,740	14.07	%
Fifth Third	1	19,048	11.79	%

Total Assets

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Total Loans

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Loan Mix
September 30,

2005	2004
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Net Charge-Offs
to Average Loans

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Peer is the 30 public bank holding companies in the Midwest nearest in size to OSBC.

Total Deposits

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Deposit Mix

September 30,

2005	2004
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Net Interest Margin

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Peer is the 30 public bank holding companies in the Midwest nearest in size to OSBC.

Efficiency Ratio

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Peer is the 30 public bank holding companies in the Midwest nearest in size to OSBC.

Non-GAAP Reconciliations

(In Thousands)

	1999			2000			2001			2002			2003			2004			Sep-05
Net Interest Margin
Interest income (GAAP)	$	66,989		$	77,141		$	84,791		$	85,491		$	87,844		$	97,398		$	87,311
Taxable-equivalent adjustment:
Loans	165			122			197			226			193			206			154
Investments	863			1,518			1,448			1,393			1,339			1,758			1,937
Interest income - FTE	68,017			78,781			86,436			87,110			89,376			99,362			89,402
Interest expense (GAAP)	29,154			35,816			35,290			28,009			25,468			29,039			32,352
Net interest income - FTE	$	38,863		$	42,965		$	51,146		$	59,101		$	63,908		$	70,323		$	57,050
Net interest income - (GAAP)	$	37,835		$	41,325		$	49,501		$	57,482		$	62,376		$	68,359		$	54,959
Interest earning assets	$	909,688		$	1,001,129		$	1,180,869		$	1,379,516		$	1,617,848		$	1,858,710		$	2,084,821
Net interest margin (GAAP)	4.16		%	4.13		%	4.19		%	4.17		%	3.86		%	3.68		%	3.52		%
Net interest margin - FTE	4.27		%	4.29		%	4.33		%	4.28		%	3.95		%	3.78		%	3.66		%
Efficiency Ratio
Noninterest expense	$	37,276		$	37,088		$	41,476		$	48,056		$	54,175		$	55,858		$	45,459
Net interest income (GAAP)	37,835			41,325			49,501			57,482			62,376			68,359			54,959
Taxable-equivalent adjustment:
Loans	165			122			197			226			193			206			154
Investments	863			1,518			1,448			1,393			1,339			1,758			1,937
Net interest income - FTE	38,863			42,965			51,146			59,101			63,908			70,323			57,050
Noninterest income	18,559			16,568			22,301			25,276			29,227			25,914			20,956
Total revenue - FTE	57,422			59,533			73,447			84,377			93,135			96,237			78,006
Efficiency ratio	64.92		%	62.30		%	56.47		%	56.95		%	58.17		%	58.04		%	58.28		%

Return on Equity

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Earnings Per Share

(Diluted Basis)

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Peer Comparison

	OSBC		Midwest		Illinois		National
Return on equity	18.67	%	13.28	%	11.62	%	13.14	%
Return on assets	1.20	%	1.09	%	.94	%	1.12	%
Net interest margin	3.66	%	3.69	%	3.47	%	4.02	%
Efficiency ratio	58.28	%	59.22	%	63.55	%	59.04	%
NPA % of assets	0.23	%	0.63	%	0.63	%	0.41	%
Charge-offs/Avg. Loans	0.04	%	0.26	%	0.16	%	0.23	%
Price to LTM earnings	15.7	x	17.0	x	16.9	x	17.9	x

Midwest: 30 public bank holding companies in the Midwest nearest in size to OSBC.

Illinois: Publicly-traded bank holding companies in Illinois.

National: All publicly traded bank holding companies.

Stock Comparison
Five Year Performance

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