The Willoughby River (/ˈwɪləbi/ WIL-ə-bee) is a tributary of the Barton River, flowing on 18.6 km (11.6 mi), in the Orleans County, Vermont, United States.

Its course runs through forested areas, agricultural and urban.

The Willoughby River rises on the northwest shore of Lake Willoughby (length: 6.9 km (4.3 mi); maximum length: 1.3 km (0.81 mi); height: 356 meters (1,168 ft)).

The southern part of the lake is surrounded by the Willoughby State Forest.

The English place name "Willoughby River" was made official October 29, 1980 to the GNIS.