On September 1, 1982, ownership and maintenance of County Route 51 (CR 51) from CR 110 north to US 11 in Winthrop was transferred from St. Lawrence County to the state of New York as part of a highway maintenance swap between the two levels of government. Also transferred to the state as part of the swap was CR 110 itself, an east–west highway extending from Stockholm Center to Coteys Corner. The segment of CR 51 given to New York became a southward extension of NY 420, which now began at NY 11C (former CR 110) and briefly overlapped US 11 in Winthrop. The alignments of US 11 and NY 11C between Stockholm Center and Coteys Corner were flipped on June 13, 1992.