Route 172 is a minor Connecticut state highway running entirely within the town of Southbury.

It officially begins at the eastbound off-ramp at exit 14 of I-84, where it also intersects Main Street South, the surface route to Southbury center.

Route 172 proceeds northward, following a C-curve route, crossing the Pomperaug River into the village of South Britain in the western part of Southbury about a mile later.

The road continues north for another three miles (5 km) before ending at an intersection with Route 67 in northern Southbury.

[1] Route 172 was created as part of the 1932 state highway renumbering from a previously unnumbered road.