The Assabet River is a small, 34.4-mile (55.4 km) long river located about 20 miles (30 km) west of Boston, Massachusetts, United States. The Assabet rises from a swampy area known as the Assabet Reservoir in Westborough, Massachusetts, and flows northeast before merging with the Sudbury River at Egg Rock in Concord, Massachusetts, to become the Concord River. The Organization for the Assabet, Sudbury and Concord Rivers, headquartered in West Concord, Massachusetts, is a non-profit organization dedicated to the preservation, protection, and enhancement of the natural and recreational features of these three rivers and their watershed. As the Concord River is a tributary of the Merrimack River, it and the Assabet and Sudbury rivers are part of the larger Merrimack River watershed.

Westborough is a town in Worcester County, Massachusetts, United States. The population was 21,567 at the 2020 Census, in over 7,000 households. Incorporated in 1717, the town is governed under the New England open town meeting system, headed by a five-member elected Board of Selectmen whose duties include licensing, appointing various administrative positions, and calling a town meeting of citizens annually or whenever the need arises.