- Western Terminus:
- I-691 and I-91 in Meriden
- Eastern Terminus:
- Boston Post Road (US 6) in Windham
- 38.38 miles
- New Haven, Middlesex, Hartford, Tolland, Windham
CT 66 is an east/west route through the center of Connecticut. I-691 turns into CT 66 at its interchange with I-91 in Meriden. The expressway continues east for a couple of exits before petering out and turning into Meriden Road. CT 66 follows Meriden Road east to Middletown, where it becomes Washington Street. A couple of blocks before the Connecticut River, CT 66 turns north onto Main Street, which curves back to the east, merges with CT 17, and crosses the river to Portland via the Arrigoni Bridge. It is perhaps the grandest bridge in the state, despite being relatively obscure. On the other side, CT 66/CT 17 turns east onto Marlborough Street, while Main Street continues as CT 17A. After about a mile, CT 17 splits off to the north as Gospel Lane, while CT 66 continues northeast through East Hampton, Marlborough, and Hebron to Willimantic. There, US 6 is an expressway bypass for a few miles. CT 66 touches US 6 at both ends of the bypass and serves as a de facto business route in between, passing through the main part of the town. CT 66 ends at US 6 at the east end of the bypass.