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.

The Columbus, Ohio metropolitan area is a metropolitan area in Central Ohio surrounding the state capital of Columbus. As defined by the U.S. Census Bureau, it includes the counties of Delaware, Fairfield, Franklin, Hocking, Licking, Madison, Morrow, Perry, Pickaway, and Union. At the 2020 census, the MSA had a population of 2,138,926, making it 32nd-most populous in the United States and the second largest in Ohio, behind the Cincinnati metropolitan area. The metro area, also known as Central Ohio or Greater Columbus, is one of the largest and fastest-growing metropolitan areas in the Midwestern United States.