Route 70 officially begins as a continuation of SR 801, known locally as Waterbury Road, at its interchange with Interstate 84 (I-84) at exit 26 in Cheshire.

Route 70 follows River Road for about 1.6 miles (2.6 km) then turns onto Main Street.

In the 1932 state highway renumbering,[2] modern Route 70 was created from old Highway 323 plus an extension east of Route 10 along a previously unnumbered road to the South Meriden section of the city of Meriden.

The original eastern terminus was at Hanover Road (then Route 71) just after crossing the Quinnipiac River.

In 1964, Route 70 was truncated in the west so that it now began at the I-84 Interchange 26 westbound onramp.