| Flat Rock | |
| Settlement Type: | Census-designated place |
| Pushpin Map: | USA Ohio |
| Pushpin Map Caption: | Location within the state of Ohio |
| Subdivision Type: | Country |
| Subdivision Name: | United States |
| Subdivision Type1: | State |
| Subdivision Name1: | Ohio |
| Subdivision Type2: | County |
| Subdivision Type3: | Township |
| Subdivision Name3: | Thompson |
| Unit Pref: | Imperial |
| Area Footnotes: | [1] |
| Area Total Km2: | 0.55 |
| Area Land Km2: | 0.55 |
| Area Water Km2: | 0.00 |
| Area Total Sq Mi: | 0.21 |
| Area Land Sq Mi: | 0.21 |
| Area Water Sq Mi: | 0.00 |
| Population As Of: | 2020 |
| Population Total: | 227 |
| Population Density Km2: | 412.76 |
| Population Density Sq Mi: | 1070.75 |
| Timezone: | Eastern (EST) |
| Utc Offset: | -5 |
| Timezone Dst: | EDT |
| Utc Offset Dst: | -4 |
| Elevation Ft: | 801 |
| Coordinates: | 41.2356°N -82.8592°W |
| Postal Code Type: | ZIP codes |
| Postal Code: | 44828 |
| Blank Name: | FIPS code |
| Blank Info: | 39-27356 |
| Blank1 Name: | GNIS feature ID |
| Blank1 Info: | 2628891 |
Flat Rock is a census-designated place in northeastern Thompson Township, Seneca County, Ohio, United States. It has a post office with the ZIP code 44828.[2] The population was 227 at the 2020 census.
Flat Rock was originally called Lewisville, and under the latter name was platted in 1841.[3] A post office called Flat Rock has been in operation since 1846.[4] The present name comes from a flat layer of rock covering an artesian aquifer.[5]