FORM 3

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 INITIAL STATEMENT OF BENEFICIAL OWNERSHIP OF SECURITIES Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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(Print or Type Responses)

1. Name and Address of Reporting Person *   Warren Brian 2. Date of Event Requiring Statement (Month/Day/Year) 09/10/2015 3. Issuer Name and Ticker or Trading Symbol CoreSite Realty Corp [COR] (Last) (First) (Middle) C/O CORESITE REALTY CORPORATION, 1001 17TH STREET, SUITE 500 4. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director _____ 10% Owner __X__ Officer (give title below) _____ Other (specify below) SVP, Products & Marketing 5. If Amendment, Date Original Filed(Month/Day/Year) (Street) DENVER, CO 80202 6. Individual or Joint/Group Filing(Check Applicable Line) _X_ Form filed by One Reporting Person ___ Form filed by More than One Reporting Person (City) (State) (Zip) Table I - Non-Derivative Securities Beneficially Owned

1.Title of Security (Instr. 4) 2. Amount of Securities Beneficially Owned (Instr. 4) 3. Ownership Form: Direct (D) or Indirect (I) (Instr. 5) 4. Nature of Indirect Beneficial Ownership (Instr. 5) Common Stock 26,337 (1) (2) (3) D Â

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.			SEC 1473 (7-02)
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Table II - Derivative Securities Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)

1. Title of Derivative Security (Instr. 4)	2. Date Exercisable and Expiration Date (Month/Day/Year)		3. Title and Amount of Securities Underlying Derivative Security (Instr. 4)		4. Conversion or Exercise Price of Derivative Security	5. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 5)	6. Nature of Indirect Beneficial Ownership (Instr. 5)
	Date Exercisable	Expiration Date	Title	Amount or Number of Shares
Stock Option (Right to Buy)	  (4)	11/17/2021	Common Stock	3,839	$ 16.41	D	Â
Stock Option (Right to Buy)	  (4)	04/05/2022	Common Stock	7,692	$ 23.99	D	Â
Stock Option (Right to Buy)	  (4)	02/28/2023	Common Stock	4,814	$ 32.4	D	Â
Stock Option (Right to Buy)	  (4)	05/02/2023	Common Stock	1,070	$ 35.62	D	Â

Reporting Owners

Reporting Owner Name / Address	Relationships
	Director	10% Owner	Officer	Other
Warren Brian C/O CORESITE REALTY CORPORATION 1001 17TH STREET, SUITE 500 DENVER, CO 80202	Â	Â	  SVP, Products & Marketing	Â

Signatures

/s/ Derek S. McCandless, Attorney-in-Fact		09/21/2015
**Signature of Reporting Person		Date

Explanation of Responses:

*	If the form is filed by more than one reporting person, see Instruction 5(b)(v).
**	Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
(1)	Includes 9,686 shares of unvested restricted stock awards granted to the reporting person under the issuer's 2010 Equity Incentive Award Plan. The unvested shares of restricted stock vest as follows: (i) 1,124 shares vest on November 24, 2015, (ii) 938 shares vest on April 5, 2016, (iii) 1,362 shares vest in two equal annual installments on February 28, 2016 and February 28, 2017, (iv) 2,521 shares vest in two equal installments on March 4, 2016 and March 4, 2017, and (v) 3,741 shares vest in three equal installments beginning on March 3, 2016, in each case provided that the reporting person remains employed by the issuer as of each vesting date.
(2)	Includes 7,830 performance-based restricted shares ("PSAs") granted under the issuer's 2010 Equity Incentive Award Plan, of which 3,465 PSAs were granted in 2014 (the "2014 PSAs") and 4,365 PSAs were granted in 2015 (the "2015 PSAs").
(3)	The number of PSAs earned is based on the issuer's achievement of relative total shareholder return ("TSR") measured versus the MSCI US REIT Index over a three-year performance period. The number of 2014 PSAs earned may range from 0% to 150% of target and the number of 2015 PSAs earned may range from 25% to 175% of target. The PSAs are earned as follows: (i) 20% of the PSAs are earned upon TSR achievement in year one of the performance period, (ii) 20% of the PSAs are earned upon TSR achievement in year two of the performance period, (iii) 20% of the PSAs are earned upon TSR achievement in year three of the performance period, and (iv) 40% of the PSAs are earned upon a cumulative TSR achievement over the three-year performance period, subject to the reporting person's continued employment with the issuer at the end of the three-year performance period. The PSAs are granted and issued at the maximum percentage of the target amount.
(4)	The stock options were granted under the issuer's 2010 Equity Incentive Award Plan and vest and become exercisable in four equal annual installments beginning on the first anniversary of the grant date, provided that the reporting person remains employed by the issuer as of each vesting date.

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