| Official Name: | Mamanasco Lake, Connecticut |
| Settlement Type: | Census-designated place |
| Pushpin Map: | Connecticut#USA |
| Pushpin Label: | Mamanasco Lake |
| Coordinates: | 41.3186°N -73.525°W |
| Subdivision Type: | Country |
| Subdivision Type1: | State |
| Subdivision Name1: | Connecticut |
| Subdivision Type2: | County |
| Subdivision Name2: | Fairfield |
| Subdivision Type3: | Town |
| Subdivision Name3: | Ridgefield |
| Area Footnotes: | [1] |
| Area Total Km2: | 1.41 |
| Area Land Km2: | 1.06 |
| Area Water Km2: | 0.35 |
| Population As Of: | 2020 |
| Timezone: | Eastern (EST) |
| Utc Offset: | -5 |
| Timezone Dst: | EDT |
| Utc Offset Dst: | -4 |
| Elevation Ft: | 578 |
| Postal Code Type: | ZIP Code |
| Postal Code: | 06877 (Ridgefield) |
| Area Code: | 203/475 |
| Blank Name: | FIPS code |
| Blank Info: | 09-44660 |
| Blank1 Name: | GNIS feature ID |
| Blank1 Info: | 2805954 |
Mamanasco Lake is a census-designated place (CDP) in the town of Ridgefield, Fairfield County, Connecticut, United States. It is northwest of the center of Ridgefield and surrounds a lake of the same name.
Mamanasco Lake was first listed as a CDP prior to the 2020 census.