Union County is a county located in the U.S. state of Ohio. As of the 2020 census, the population was 62,784. Its county seat is Marysville. Its name is reflective of its origins, it being the union of portions of Franklin, Delaware, Madison, and Logan counties.

Mary Jo Kilroy is an American attorney and politician who served as the U.S. representative for Ohio's 15th congressional district from 2009 until 2011. She is a member of the Democratic Party from Ohio. She was defeated in her November 2, 2010 re-election bid. In 2012, she ran in the newly redrawn, Columbus-based 3rd congressional district but lost in the primary.