The road runs along the east bank of the lower Naugatuck River.

It enters the city of Ansonia after 0.8 miles (1.3 km), becoming Main Street.

In Seymour, it becomes South Main Street, meeting and briefly overlapping Route 313 (for Woodbridge and New Haven) then ending 0.2 miles (0.32 km) later at an intersection with Route 67 near the Seymour railroad station.

[1] The entire length of Route 115 is also designated as Veterans Memorial Highway.

[3] In the 1920s, the route through Derby, Ansonia, and Seymour on the east bank of the Naugatuck River was designated as State Highway 200.