Historically, the name Minisink, which dates to the mid 17th century, has applied to a much larger area than the current town, running as far north as Minisink Ford, twenty miles northwest of present day Minisink, south to the Delaware Water Gap, thirty miles southwest of present day Minisink, and from the Kittatinny Ridge to the east to the Poconos to the west (See ). The Minisink Patent, granted in 1704, was a somewhat smaller area, but still far larger than the present town, which was given its present boundaries in 1800. Adding to the confusion is the fact that the New York - New Jersey border was previously seven or eight miles north of its present location: Minisink used to be in New Jersey.
First settled by Europeans around 1725, the jurisdiction was organized by Americans as a town in 1788 following the Revolutionary War. In the following decades, the Town of Minisink lost territory to newer towns: Deer Park (1798), Wawayanda (1849), and Greenville (1853). In 1871, the community of Unionville set itself off from the town by incorporating as a village.