CoreSite Realty DEFA14A Additional proxy soliciting materials

UNITED STATES
SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549
SCHEDULE 14A
Proxy Statement Pursuant to Section 14(a) of the Securities Exchange Act of 1934 (Amendment No.     )
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o	Definitive Proxy Statement
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o	Soliciting Material under §240.14a-12
CORESITE REALTY CORPORATION
(Name of Registrant as Specified In Its Charter)
(Name of Person(s) Filing Proxy Statement, if other than the Registrant)
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*** Exercise Your Right to Vote *** Important Notice Regarding the Availability of Proxy Materials for the Stockholder Meeting to Be Held on May 16, 2019 CORESITE REALTY CORPORATION You are receiving this communication because you hold shares in the above named company. This is not a ballot. You cannot use this notice to vote these shares. This communication presents only an overview of the more complete proxy materials that are available to you on the Internet. You may view the proxy materials online at www.proxyvote.com or easily request a paper copy (see reverse side). We encourage you to access and review all of the important information contained in the proxy materials before voting. CORESITE REALTY CORPORATION 1001 17TH STREET, SUITE 500 DENVER, CO 80202 0000412700_1 R1.0.1.18 See the reverse side of this notice to obtain proxy materials and voting instructions. Meeting Information Meeting Type: Annual Meeting For holders as of: March 14, 2019 Date: May 16, 2019Time: 2:00 PM EDT Location: Sheraton Reston Hotel 11810 Sunrise Valley Drive Reston, Virginia 20191

Before You Vote How to Access the Proxy Materials Proxy Materials Available to VIEW or RECEIVE:  Have the information that is printed in the box marked by the arrow (located on the  by the arrow (located on the following page) in the subject line. How To Vote Please Choose One of the Following Voting Methods possession  available and follow the instructions. marked by the arrow 0000412700_2 R1.0.1.18 Vote In Person: Many stockholder meetings have attendance requirements including, but not limited to, the of an attendance ticket issued by the entity holding the meeting. Please check the meeting materials for any specia requirements for meeting attendance. At the meeting, you will need to request a ballot to vote these shares. Vote By Internet: To vote now by Internet, go to www.proxyvote.com. Have the information that is printed in the box Vote By Mail: You can vote by mail by requesting a paper copy of the materials, which will include a proxy card. l 1. Form 10-K2. Notice & Proxy Statement3. Letter to Shareholders How to View Online: following page) and visit: www.proxyvote.com. How to Request and Receive a PAPER or E-MAIL Copy: If you want to receive a paper or e-mail copy of these documents, you must request one. There is NO charge for requesting a copy. Please choose one of the following methods to make your request: 1) BY INTERNET:www.proxyvote.com 2) BY TELEPHONE:1-800-579-1639 3) BY E-MAIL*:sendmaterial@proxyvote.com * If requesting materials by e-mail, please send a blank e-mail with the information that is printed in the box marked Requests, instructions and other inquiries sent to this e-mail address will NOT be forwarded to your investment advisor. Please make the request as instructed above on or before May 02, 2019 to facilitate timely delivery.

The Board of Directors recommends you vote FOR the following: 1. Election of Directors Nominees 01 Robert G. Stuckey 06 Michael R. Koehler 02 Paul E. Szurek 07 J. David Thompson 03 James A. Attwood, Jr.04 Jean A. Bua 08 David A. Wilson 05 Kelly C. Chambliss The Board of Directors recommends you vote FOR proposals 2 and 3. 2. Ratification of the appointment of KPMG LLP as our independent registered public accounting firm for the fiscal year ending December 31, 2019. 3. The advisory vote to approve the compensation of our named executive officers. NOTE: Such other business as may properly come before the meeting or any adjournment thereof. 0000412700_3 R1.0.1.18 Voting items

0000412700_4 R1.0.1.18