- Western Terminus:
- New York-Connecticut state line
- Eastern Terminus:
- Connecticut-Rhode Island state line
- 116.33 miles
- Fairfield, New Haven, Litchfield, Hartford, Tolland, Windham
US 6 is a major east/west route crossing the country from Bishop, California, to Provincetown, Massachusetts. It is one of the longest routes in the country, longer than any interstate highway. It enters Connecticut from New York multiplexed with US 202 along Mill Plain Road, which runs parallel to and north of the Yankee Expressway (I-84). After a couple of miles, US 7 joins the expressway and it curves to the north. US 6/US 202 joins the expressway as well one exit later. The four-way multiplex lasts for a few exits before US 7/US 202 splits off to go north toward New Milford. US 6 continues to follow I-84 for one more exit before splitting off and running east as a surface road to Newtown. There is rejoins the I-84 as it crosses the Housatonic River to New Haven County.
On the other side of the river, US 6 splits off from I-84 in Southbury and runs north into Litchfield County, where it curves to the northeast toward Thomaston. There, it joins the CT 8 expressway for one exit and then splits off to runs east to Farmington, where it joins the Yankee Expressway (I-84) yet again. It follows the expressway through Hartford and across the Connecticut River. In Manchester, it splits off onto Middle Turnpike West (US 44). US 6 and US 44 are multiplexed through Manchester to Bolton, where I-384 has its eastern terminus. I-384 merges into US 6/US 44, and then the two routes split. US 6 runs southeast toward Willimantic, where it becomes an expressway running north of the town while CT 66 runs through the town. The expressway ends heading out of Willimantic, and US 6 continues east as a surface road to the border with Rhode Island.