In 1923, the New York State Legislature passed a law authorizing the construction of a highway connecting Route 24 (an unsigned legislative route that is now part of NY 30) to the new Veterans' Mountain Camp, an American Legion camp on Tupper Lake. The work was funded through appropriations defined in the law. The beginning of a state road to the camp came in 1924 when earth movers were brought in by the Harnathy Contracting Company, with construction beginning in early June. The project would include construction of a concrete bridge over the Bog River. However, Hanrathy was unable to finish the job as it went bankrupt, and a second firm, the Spadaccini Realty Construction Corporation of The Bronx was brought into finish the job, which began in June 1925. The bridge over the Bog River was completed on August 29, 1925 and they announced would be opened for traffic within ten days. The route finally opened in 1925, with the Veterans Camp opening on May 15, 1926. This road was extended from modern NY 30 north to a dead end at Warren Point. In the 1930 renumbering of state highways in New York, hundreds of state-maintained highways that did not yet have a designation were assigned one. The Veterans' Mountain Camp highway was designated as NY 421 by the following year.