| Official Name: | Mercerville, Ohio |
| Pushpin Map: | Ohio#USA |
| Pushpin Label: | Mercerville |
| Subdivision Type: | Country |
| Subdivision Name: | United States |
| Subdivision Type1: | State |
| Subdivision Name1: | Ohio |
| Subdivision Type2: | County |
| Subdivision Name2: | Gallia |
| Timezone: | Eastern (EST) |
| Utc Offset: | -5 |
| Timezone Dst: | EDT |
| Utc Offset Dst: | -4 |
| Elevation Ft: | 768 |
| Coordinates: | 38.6625°N -82.2719°W |
| Area Code: | 740 & 220 |
| Blank Name: | GNIS feature ID |
| Blank Info: | 1076378 |
Mercerville is an unincorporated community in Gallia County in southern Ohio, approximately 7miles north of Crown City and 25miles northeast of Huntington, West Virginia, near the easternmost corner of Wayne National Forest and roughly 5miles west of the Ohio River, where Ohio borders West Virginia. Mercerville sits along State Route 218 (SR 218) near its intersection with SR 790. It is home to South Gallia High School and nearby Hannan Trace Elementary School.
Mercerville is often mistaken for Crown City because Mercerville does not have its own US Post Office, much in the same way that nearby Rio Grande, Ohio, mailing addresses all say Bidwell.