The Greenwood Lake–Goshen portion of NY 17A was originally designated as part of New York State Route 55 in the 1920s. South of Greenwood Lake, NY 55 used modern NY 210. NY 55 was split into NY 17A and NY 210 as part of the 1930 renumbering of state highways in New York. Initially, only NY 210 continued east from Greenwood Lake to Southfields; however, NY 17A was extended to Southfields by 1933, overlapping NY 210. The overlap was eliminated in 1982 when NY 210 was truncated to Greenwood Lake.