Remsen was named for Henry Remsen II, the original proprietor of the township and the inheritor of the Remsenburgh patent, which embraced some in Oneida and Herkimer counties and was granted in 1766 (later regranted by the Legislature in 1787) to Remsen and four other New York merchants. Remsen, a New York City merchant and owner of Henry Remsen Jr. & Co., was the descendant of some of the earliest Dutch settlers of New Amsterdam.
The town was first settled around 1792, when Barnabas Mitchell of Meriden, Connecticut settled in the area and began clearing a farm which was subsequently owned by his son Milo, and became known as the 'Milo Mitchell place.' Soon afterwards, Mitchell was joined by Nathaniel Rockwood, John Bonner, Perez Farr, Bettis Le Clerc, Jonah Dayton, John Kent and Shubael Cross, all of whom came from New England to settle in Remsen. In September 1795 five families from Wales settled in the vicinity, marking the beginning of a substantial Welsh presence in the area. The Town of Remsen was formed in 1798 from part of the Town of Norway in Herkimer County, New York when Oneida County was formed. In 1869, part of Remsen was used to form the new Town of Forestport.