Area code 914

914 was among the original area codes, which were announced in October 1947. It originally was assigned to most of the New York state side of the New York metropolitan area The 914 code originally included Nassau, Suffolk, Rockland, Putnam, Orange, Dutchess, Ulster, Sullivan and Delaware counties, plus Westchester. In 1951, Nassau and Suffolk were transitioned to area code 516.
Due to the growing popularity and commercialization of cell phones and internet dial-up connections, 914 was split on June 5, 2000. Westchester retained 914, while the rest of the region became 845. 914 was retained for all cell phones in the lower Hudson Valley that were in use before the split.

Wikipedia