NY 304 was assigned as part of the 1930 renumbering of state highways in New York. The route was originally an at-grade highway for its entire length, following what is now East Washington Avenue (CR 35), Middletown Road (CR 33) from Pearl River, and Main Street to West Nyack Road (then NY 59) in Nanuet. Here, NY 304 turned east, overlapping with NY 59 to access its current alignment. Farther north, NY 304 originally utilized North Main Street (CR 29) in New City and Haverstraw (CR 29) and South Mountain (CR 90) roads from New City to US 9W in Haverstraw. NY 304 was realigned slightly in the early 1940s to follow East Central Avenue in Pearl River and the overlap with NY 59 was eliminated in the mid-1950s when NY 59 was moved onto a new highway paralleling West Nyack Road to the south.