Union County is a county located in the southern part of the U.S. state of Iowa. As of the 2020 Census, the population was 12,138. The county seat is Creston. Organized at a time of tensions before the Civil War, the county was named in 1853 for the union that people wanted to preserve. Union County peaked in population at the 1900 Census. Its economy is based on agriculture and related industries.

Creston is a city in and the county seat of Union County, Iowa. The population was 7,536 at the time of the 2020 Census.