Willimantic
- Country: United States
- State: Connecticut
- Population: 17,737 (2010)
- Latitude: 41° 42.6' N (41.71065°)
- Longitude: 72° 12.5' W (-72.20813°)
- Elevation: 68 m/222 ft. above sea level
- Time zone: America/New_York (UTC -05:00); DST observed (UTC -04:00)
- Alternate names: Willimantic CDP, Thread City, Wallamantuck, Walumantticuk, Waramantick, We-am-man-tuck, Wewemantick