
Union County
- State:
- Ohio
- County Seat:
- Marysville
Union County's estimated 2025 population is 75,159 with a growth rate of 3.81% in the past year according to the most recent United States census data. Union County is the 33rd largest county in Ohio. The 2010 population was 52,462 and has seen a growth of 43.26% since that time.