US 6 enters Connecticut paired with US 202 from the town of Southeast, New York, just east of the village of Brewster.

After exiting I-84 in Southbury, US 6 once again becomes a surface road and is duplexed with Route 67 for 2.7 miles (4.3 km).

After leaving the Route 8 freeway, US 6 continues as an alternating two- and four-lane surface road through the towns of Plymouth, Bristol, and Farmington.

After crossing the town line, the eastbound and westbound sides of US 6 split, with a hill in between them.

At this point, Hop River State Park Trail passes under both sides of the freeway.

Soon after the eastbound entrance ramp joins US 6, the freeway crosses the Natchaug River and once again enters Windham.

Just before the Rhode Island state line, SR 695, the unsigned portion of the Connecticut Turnpike, merges into US 6 eastbound as it enters the town of Foster.

US 6, on the other hand, went east from Brewster on its current alignment, meeting with Route 3 in downtown Danbury.

Construction had been planned to begin in the late 1980s, but federal, state, and local officials could not reach an agreement on a feasible route that avoided the Hop River wetlands and development within the towns of Andover, Bolton, Coventry, and Columbia.

The Environmental Protection Agency, U.S. Army Corps of Engineers (USACE), and Federal Highway Administration (FHWA) favored a southerly alignment (Alternative 133 18/25) that would cut through residential and commercial areas as well as the Hop River's adjoining wetlands.

State and local officials continued to press USACE to approve the northern alignment.

In 2007, CTDOT began making safety improvements and capacity upgrades to the existing US 6 through Andover, Bolton, and Columbia.