Route 77 crosses US 1 and I-95 (at exit 58), becoming the main road through the northern part of Guilford, past Lake Quonnipaug.

It has a junction with Route 80 (leading to Killingworth and North Branford) about 5.4 miles (8.7 km) north of I-95, then crosses into the town of Durham, where the road changes name to Guilford Road.

The entire route is classified as a collector road and carries average daily traffic volumes of about 5,900 vehicles.

[1] Route 77 is a designated state scenic road for its entire length.

In 1922, Connecticut took over the maintenance of the main through routes and State Highway 112 was established, incorporating the old turnpike alignment from Guilford to Durham and extending north beyond Durham into Middletown (along modern Route 17).