The White Plains Armory is a historic building in White Plains, New York, in Westchester County. Located at 65 Mitchell Place/35 South Broadway, the building was built to serve as a National Guard armory. Construction of the building began in 1909 and was completed in 1910. The building was designed by architect James E. Ware. The building was 31,612 square feet and takes up three-quarters of an acre. 49th Separate Company/Company L, 10th Infantry Regiment occupied the armory from 1910 to 1939. From April 1924 to November 1929, the White Plains Armory was the temporary headquarters of Troop K of the New York State Police, after a March 3, 1924 fire destroyed the troop's headquarters at Gedney Farms. The police troop left the Armory in November 1929 after a new headquarters in Hawthorne was