Thomas J. "Tom" Dart is the current Sheriff of Cook County, Illinois. His department is the second largest in the United States after the Los Angeles County Sheriff's Department.

Dart began his career a state prosecutor in Cook County. He then served as state representative as a Democrat for Illinois' 28th House District from January 1993 until January 2003, before becoming chief of staff to Cook County Sheriff Michael F. Sheahan. In November 2002, Dart was the Democratic nominee for state treasurer of Illinois but lost to incumbent Republican Judy Baar Topinka.

When Sheahan announced his retirement in 2006, Dart announced his candidacy to succeed him. Dart won the Democratic primary election on March 21, 2006, defeating Sylvester Baker and Richard Remus by a wide margin, and won the general election in November 2006.