Union County is the name of seventeen counties in the United States:
- Union County, Arkansas
- Union County, Florida
- Union County, Georgia
- Union County, Illinois
- Union County, Indiana
- Union County, Iowa
- Union County, Kentucky
- Union County, Mississippi
- Union County, New Jersey, the most populous Union County in the country
- Union County, New Mexico
- Union County, North Carolina
- Union County, Ohio
- Union County, Oregon
- Union County, Pennsylvania
- Union County, South Carolina
- Union County, South Dakota
- Union County, Tennessee