Exhibit 16.1

Ernst & Young LLP
8484 Westpark Drive
McLean, VA 22102

Tel: (703) 747-1000
www.ey.com

May 7, 2010

Securities and Exchange Commission
100 F Street, N.E.
Washington, DC 20549

Ladies and Gentlemen:

We have read the draft Form S-11 dated May 7, 2010 expected to be filed with the Securities and Exchange Commission on or about May 10, 2010, of CoreSite Realty Corporation and its subsidiaries and are in agreement with the statements contained in the second and fourth paragraphs under the heading “Change in Independent Registered Accounting Firm” therein. We have no basis to agree or disagree with other statements of the registrant contained therein.