Route 85 was commissioned in 1932 from the old SH 102 (New London to Colchester) and SH 366 (Hebron to Bolton). The portion south of Colchester follows the 19th-century New London Turnpike road.

Its original alignment, from south to north:

• Broad Street in New London, from Huntington Street to Colman Street (now a local road)
• Broad Street north of Colman Street (now part of today's Route 85); continuing along modern Route 85 to Old Amston Road in Colchester
• Old Amston Road to Amston Road (straightened around 1944)
• Amston Road and Church Street (modern Route 85) to Route 66 in Hebron
• Marjorie Circle in Hebron, bypassed around 1960
• Gilead Street (modern Route 85) to Martin Road
• Martin Road and Porter Road back to Gilead Street
• Prentice Hill Road and Salt Box Road are also old alignments
• North Street in Hebron and West Street in Bolton to Camp Meeting Road (SR 534)
• modern SR 534 to end at Route 83 in South Manchester

Proposed Freeway becomes Route 11

Statewide plans in the 1950s included a freeway connecting Hartford and New London, using Routes 2 and 85. The Route 85 freeway would extend from Route 2 in Colchester to US 1 in Waterford.

Part of this road was built in 1972, from Route 2 in Colchester to Route 82 in Salem. In July 1971, however, the DOT had announced that in order to minimize motorist confusion and signing costs, the old Route 85 would keep its number. The new Route freeway opened as Route 11, and there's much more history on the Route 11 page.

Manchester and Bolton

The Route 83/85 intersection in Manchester might have been signed up to 1963; but state maintenance for Route 85 was truncated at the Bolton town line in 1950, and had been removed from Route 83, between Route 2 and US 6, for many years.

At noon on Mar. 29, 1963, Route 85's north end was moved to end at US 6/44 in Bolton. It took over former SR 807 (Clark Road and Bolton Center Road); and the leftover portion including Camp Meeting Road became SR 534. The state had announced the planned change about a year earlier.

Hebron

In 1960, about 5 miles of Route 94 and Route 85 were reconstructed in the Gilead area of Hebron. Salt Box Road and Prentice Hill Road are old alignments of the route. Porter Road and Martin Road are also older alignments where a sharp corner was bypassed. The state briefly assigned SR 527, 527A, 527B, 527C, and 527D to the old segments of the route.

The intersection at Route 66 in downtown Hebron was formerly a dogleg. Route 66 entered from the west along Chestnut Hill Road and Gristmill Road. Route 85 followed Marjorie Circle. Route 66 was straightened out earlier; Route 85 was realigned around 1960.

In 1966, the town of Hebron renamed several older parts of Gilead Street in the area, to Salt Box Road, Prentice Hill Road, Porter Street, and Martin Road.

Salem, Montville, and Waterford

A 1931 study by the Traffic Section Department of Motor Vehicles called for a traffic circle at the Salem intersection with Route 82. A roundabout was completed there a few years later, in 2012.

In 1984, Route 85 was widened to four lanes with a median near the newly opened Crystal Mall in Waterford.