Mark C. Poloncarz (born 1967) is the current county executive of Erie County, New York. Poloncarz, a Democrat was elected county executive on November 8, 2011 after defeating the incumbent county executive Chris Collins a Republican by a 53 - 47 percentage point margin. Poloncarz is only the 2nd Democrat to be elected to the position of county executive in the 51 year history of the position. Poloncarz was the elected comptroller of the county at the time of his election as executive.

Poloncarz was a heavy underdog when he entered the race in May of 2011. However, by focusing on key issues of properly funding libraries and arts and cultural institutions, and the failure of the Collins's administration to go after waste in the Medicaid system, Poloncarz was able to chip away a sizable Collins lead. Poloncarz also capitalized on his "son of a steelworker" blue collar background against Collins self-proclaimed businessman style to show Collins was out-of-touch with the common man.

Poloncarz was first elected comptroller in 2005 and was re-elected in 2009 in a three person race by defeating Republican Phil Kadet and Independence Party candidate Michael Abramo by a 52 - 45 - 3 percentage point margin, respectively. Prior to being elected comptroller Poloncarz was an American business and finance lawyer residing in Buffalo, New York.