| Official Name: | Williamstown, Indiana |
| Pushpin Map: | Indiana#USA |
| Pushpin Label: | Williamstown |
| Subdivision Type: | Country |
| Subdivision Name: | United States |
| Subdivision Type1: | State |
| Subdivision Name1: | Indiana |
| Subdivision Type2: | County |
| Subdivision Name2: | Decatur, Rush |
| Subdivision Type3: | Township |
| Subdivision Name3: | Clinton, Anderson |
| Timezone: | Eastern (EST) |
| Utc Offset: | -5 |
| Timezone Dst: | EDT |
| Utc Offset Dst: | -4 |
| Coordinates: | 39.4528°N -85.4692°W |
| Elevation Ft: | 958 |
| Postal Code Type: | ZIP code |
| Postal Code: | 47240 |
| Blank Name: | FIPS code |
| Blank Info: | 18-84446[1] |
| Blank1 Name: | GNIS feature ID |
| Blank1 Info: | 446089 |
Williamstown is an unincorporated community in Decatur and Rush counties, in the U.S. state of Indiana.
Williamstown was founded in 1830.[2] An old variant name of the community was called Earl City.
A post office was established at Williamstown in 1834, and remained in operation until it was discontinued in 1905.[3]
Williamstown is located at the boundary between Decatur and Rush counties.[4]