Mansfield Hollow Lake is a reservoir resting on the border of Windham County and Tolland County, Connecticut. It was created by the Mansfield Hollow Dam and is entirely contained within Mansfield Hollow State Park and the Mansfield Hollow Wildlife Area. Designed and constructed by the United States Army Corps of Engineers, this dam substantially reduces flooding along the Quinebaug, Shetucket, and Thames rivers. Construction of the project began in 1949 with completion in 1952 at a cost of US$6.5 million. The Mansfield Hollow reservoir is located within the Shetucket River Watershed and is part of the Thames River Basin.