portion of modern NY 436 between Portageville Road northeast of Portageville and NY 408 in Nunda was originally designated as part of Route 43, an unsigned legislative route, by the New York State Legislature in 1911. The route also included the section of modern NY 408 linking Nunda to Mount Morris. On March 1, 1921, the route was extended southwestward along what is now NY 436 to meet Route 16 (now NY 19A) in Portageville. When the first set of posted routes in New York were assigned in 1924, no part of today's NY 436 was assigned a designation; in fact, by 1926, only two segments were state-maintained: the piece originally designated as part of legislative Route 43 and the section that now overlaps with NY 19A. In the 1930 renumbering of state highways in New York, the Portageville–Nunda leg of former legislative Route 43 became part of the new NY 39, which continued west to the now-hamlet of Pike along Griffith Road and east on current NY 436 to Dansville. Also assigned as part of the renumbering was NY 245, a route extending from then-NY 39 in Pike to Perry Center on modern NY 39 and NY 246. NY 245 was rerouted to follow a new highway (modern NY 39) northeast from Perry to a new terminus at Pine Tavern. The alignments of NY 39 and NY 245 east of Pike were mostly swapped , placing NY 39 on its modern alignment and NY 245 on the east–west highway linking Portageville to Dansville. NY 245 initially bypassed Griffith Road by way of NY 436's modern routing on NY 19A and Denton Corners Road; however, NY 245 was reconfigured to use NY 39's old alignment along Griffith Road instead by 1947. NY 245 was routed off Nunda–Dansville Road for a brief period during the 1950s. It was realigned in the late 1940s to follow NY 408 north from Nunda to the hamlet of Brooks Grove, where it would continue to Dansville by way of overlaps with NY 258 and NY 36. NY 245 was returned to its original alignment between the two locations in the late 1950s. The Pike–Dansville portion of NY 245 remained virtually unchanged until August 1971, when NY 245 was truncated to begin at its junction with NY 21 in Naples. The former routing of NY 245 between Pike and Dansville was subsequently redesignated as NY 436.