The turnpike, which was in operation from the early to the mid-19th century, was a major transportation route at the time, connecting several local communities to Litchfield County, Connecticut, and the city of Poughkeepsie.

[4] When NY 343 crosses the state line, it becomes Connecticut's Route 343 and passes through more rural and residential areas.

The road heads eastward into the town of Washington, intersecting an old alignment of NY 82 and passing to the south of Millbrook Golf and Tennis Club.

The highway passes south of the creek, Mill Brook, entering the hamlet of Littlerest, where it turns to the southeast at an intersection with County Route 99 (CR 99).

At the intersection with CR 23, NY 343 again changes direction, this time to the northeast, and soon crosses Stone Church Brook in the hamlet of Mutton Hollow.

Here, NY 343 changes directions a third time, traveling to the southeast once again towards the hamlet of Dover Plains.

[7] Northwest of Dover Plains, NY 343 turns to the northeast and passes into the town of Amenia.

The roads parallel the Tenmile River and soon intersect with CR 81 (a former routing of NY 22) south of the hamlet of Wassaic.

[8][9] When NY 343 crosses the state line into the town of Sharon, it enters a moderately rural area where a large factory is located.

[10] The alignment used by modern NY 343 was a major transportation route that passed through the colonial settlements of Wassaic and Amenia.

The highway helped General George Washington's troops during the American Revolutionary War and was also the main supply route to the hamlets of Payne's Corners (now Amenia), Washiac (now Wassaic) and Dover Plains.

[15] In 1806, a branch route, splitting off from the mainline at South Millbrook, was established to connect the hamlet of Dover Plains to Poughkeepsie.