North of Route 80, the road becomes known as Higganum Road, intersecting with Route 148 north of the town center before crossing into the town of Haddam. In Haddam, Route 81 is known as Killingworth Road and has an interchange with Route 9 at exit 9 before ending at an intersection with Route 154 in the village of Higganum.
North of Route 80, the road transitions to Higganum Road, intersecting with Route 148 north of the town center before entering Haddam. In Haddam, Route 81 is known as Killingworth Road and connects to Route 9 at exit 9 before ending at an intersection with Route 154 in the village of Higganum.