Union County IA Courthouse – Scott Romine, CC BY-SA 4.0 – Wikimedia Commons Union County is located in Iowa. About 12,138 people live here (as of 2020). Between 2010 and 2020, the population declined from 12,534 to 12,138. The area covers about 1,103.0 square kilometers. The region is divided into 6 Municipalities. The region was founded in 1853. The name originates from United States (country located primarily) Union County is county in Iowa, United States. More information at www.unioncountyiowa.org.