The Assabet River National Wildlife Refuge is a 2,230-acre (9.0 km2) protected National Wildlife Refuge located approximately 25 miles (40 km) west of Boston and 4 miles (6.4 km) west of the Eastern Massachusetts National Wildlife Refuge Complex Headquarters, along the Assabet River. It is located in portions of the towns of Hudson, Maynard, Stow and Sudbury. The Assabet River National Wildlife Refuge consists of two separate pieces of land. The larger northern section is just north of Hudson Road, extending north to the Assabet River. The southern section is located to the south of Hudson Road. There is a visitor center located in the northern section on Winterberry Way.

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.