It is a two-lane rural collector road throughout its entire length, following the path of the Mount Hope River.

Route 89 begins at an intersection with Route 195 in the village of Mansfield Center as Warrenville Road and heads north through the northeast portion of the town of Mansfield.

Along the way it passes by the north side of Mansfield Hollow Lake then runs parallel to Mount Hope River as it heads into the town of Ashford.

[1] The road connecting Willimantic to Union via Mansfield Center and Westford was designated as State Highway 146 in 1922.

In the 1932 state highway renumbering, State Highway 146 was renumbered to Route 89,[2] with a southward extension from Willimantic to Lebanon, ending at modern Route 87.