New York State Route 343 (NY 343) is a state highway located entirely within central Dutchess County, in the Hudson Valley region of the U.S. state of New York. It runs east–west from the intersection of NY 82 in the village of Millbrook to the Connecticut state line in the town of Amenia, where it continues eastward briefly as Connecticut Route 343. In Connecticut, Route 343 stretches for 1.50 miles (2.41 km) into the town of Sharon, Connecticut, where it terminates at a junction with Route 4 and Route 41. Along the way, NY 343 has a 7.3-mile (11.7 km) concurrency with NY 22 from vicinity of the hamlet of Dover Plains to the hamlet of Amenia. The entirety of modern Route 343 was originally the Dover branch of the Dutchess Turnpike, which was in operation from the early to the mid-19th century. NY 343 was designated in 1930, connecting the hamlet of Amenia to the state line, but was relocated a few years later onto the portion of New York State Route 200 from South Millbrook to the hamlet of Dover Plains. The NY 200 designation was transferred to NY 343's original alignment. NY 343 absorbed NY 200 in the early 1940s, creating an overlap with NY 22 between Dover Plains and Amenia. The Connecticut portion of the highway was originally designated as part of Route 4; however, it was renumbered to Route 343 in 1932.

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