X0306 4 2015-08-18 0 0001402057 CDW Corp CDW 0001182031 FINNEGAN PAUL J C/O MADISON DEARBORN PARTNERS, LLC 70 W. MADISON STREET, SUITE 4600 CHICAGO IL 60602 1 0 1 0 Common Stock, par value $0.01 2015-08-18 4 S 0 6550571 38.25 D 13104898 I See footnotes Consists of 4,275,998 shares sold by Madison Dearborn Capital Partners V-A, L.P. ("MDP A"), 1,134,348 shares sold by Madison Dearborn Capital Partners V-C, L.P. ("MDP C"), 42,966 shares sold by Madison Dearborn Capital Partners V Executive-A, L.P. ("MDP Exec") and 1,097,259 shares sold by MDCP Co-Investor (CDW), L.P. ("MDP Co-Investor") in an underwritten secondary offering. This sale price reflects the public offering price. The price received by the reporting persons will be reduced by the underwriters' commission of $0.25 per share. Consists of 8,554,448 shares held directly by MDP A, 2,269,348 shares held directly by MDP C, 85,955 shares held directly by MDP Exec and 2,195,147 shares held directly by MDCP Co-Investor. MDP V is the general partner of MDP A, MDP C, MDP Exec and MDP Co-Investor. MDP is the general partner of MDP V. As the sole members of a limited partner committee of MDP V that has the power, acting by majority vote, to vote or dispose of the shares directly held by MDP A, MDP C, MDP Exec and MDP Co-Investor, Paul J. Finnegan and Samuel M. Mencoff may be deemed to have shared voting and investment power over such shares. Each of Messrs. Finnegan and Mencoff and MDP V hereby disclaims any beneficial ownership of any shares held by MDP A, MDP C, MDP Exec and MDP Co-Investor except to the extent of its or his pecuniary interest therein. The record and other beneficial beneficial owners of the reported securities have separately filed a Form 4. /s/ James S. Rowe, under Power of Attorney 2015-08-20