The Old Nassau County Courthouse, also known as the Nassau County Courthouse and the Historic Nassau County Courthouse, is an historic 2-story courthouse building located at 1550 Franklin Avenue in Garden City, Nassau County, New York. Designed by noted New York City architect William B. Tubby in the Classical Revival style of architecture with a grand rotunda capped by a white dome, it was built of poured-in-place reinforced concrete. Then governor Theodore Roosevelt laid its cornerstone in 1900 and it was finished in 1901. Wings designed by Tubby were added in 1916. Later additions and renovations were 1924-1928 under the supervision of architect William J. Beardsley, who had designed the Dutchess County Court House in Poughkeepsie.