Route 171 is a state highway in northeastern Connecticut, running from Union to Putnam.

In Woodstock, it heads southeast, then turns northeast, briefly overlapping Route 198 before continuing.

It then passes Toutant Airport and turns east, briefly overlapping Route 169 before cutting across the southwest corner of Thompson into Putnam.

Old Highway 183 continued south of Woodstock Valley to Eastford along modern Route 198.

On January 1, 1959, Route 91 was renumbered as a result of the designation of Interstate 91 to avoid a numbering conflict.