DeWitt is a town (township) in Onondaga County, New York, USA. DeWitt was part of the Central New York Military Tract. The first settlers arrived around 1789. The original Erie Canal progressed through the town in 1825. DeWitt was formed in 1835 from the Town of Manlius and was named in honor of Moses DeWitt, a Major in the militia, judge of the county courts and one of the first settlers of the county.