Ownership Submission
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 *
  Rockwood Robert K.
 2. Date of Event Requiring Statement (Month/Day/Year)
05/16/2012		 3. Issuer Name and Ticker or Trading Symbol
CoreSite Realty Corp [COR]
(Last)
(First)
(Middle)
C/O CORESITE REALTY CORPORATION, 1050 17TH STREET, SUITE 800		 4. Relationship of Reporting Person(s) to Issuer
(Check all applicable)
_____ Director _____ 10% Owner
__X__ Officer (give title below) _____ Other (specify below)
SVP & General Manager
 5. If Amendment, Date Original Filed(Month/Day/Year)
(Street)

DENVER, CO 80265		 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 30,191 (1)
D
 

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)   (2) 09/22/2020 Common Stock 18,750 $ 16 D  
Stock Option (Right to Buy)   (2) 03/11/2021 Common Stock 14,447 $ 15.23 D  
Stock Option (Right to Buy)   (2) 04/05/2022 Common Stock 12,821 $ 23.94 D  
Operating Partnership Units 09/28/2011   (3) Common Stock 16,622 $ (4) D  

Reporting Owners

Reporting Owner Name / Address Relationships
Director 10% Owner Officer Other
Rockwood Robert K.
C/O CORESITE REALTY CORPORATION
1050 17TH STREET, SUITE 800
DENVER, CO 80265		       SVP & General Manager  

Signatures

/s/ Derek S. McCandless, Attorney-in-Fact 05/25/2012
**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 23,557 shares of unvested restricted stock awards granted to the reporting person under the issuer's 2010 Equity Incentive Plan. The unvested restricted stock vests as follows: (i) 6,271 shares vest in two equal installments on September 28, 2012 and September 28, 2013, (ii) 3,750 shares vest in three equal annual installments on September 28, 2012, September 28, 2013 and September 28, 2014, (iii) 4,727 shares vest in three equal annual installments on March 11, 2013, March 11, 2014 and March 11, 2015, (iv) 2,556 shares vest on March 5, 2013 and (v) 6,253 shares vest in four equal installments beginning on April 5, 2013, in each case provided that the reporting person remains employed by the issuer as of each vesting date.
(2) The stock options vest and become exercisable in four equal annual installments beginning on first anniversary of the grant date, provided that the reporting person remains employed by the issuer as of each vesting date.
(3) The Operating Partnership Units have no expiration date.
(4) The Operating Partnership Units are redeemable for cash or, at the option of the issuer, exchangable into shares of the issuer's common stock on a one-for-one basis.

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