Sempronius is a town in Cayuga County, New York, United States. The population was 895 at the 2010 census. The town was named after a Roman military and political leader by a clerk interested in the classics. Sempronius is in the southeast part of the county, southeast of Auburn.
Sempronius was part of the Central New York Military Tract. The first settler arrived around 1793. Sempronius became a town in 1799, but its area was later reduced by the formation of newer towns: Marcellus (Onondaga County) in 1804, Moravia and Niles in 1833.