During King William's War, Major Benjamin Church led his third expedition east from Boston in 1692.

The area was covered by the land patent given by the English Crown to Pilgrim governor William Bradford and his associates.

[4] In 1754, Fort Halifax was built by order of the Massachusetts General Court on the peninsula at the confluence of the Sebasticook and Kennebec rivers.

A settlement subsequently sprang up under its protection, and was named in honor of General John Winslow, of Marshfield, Massachusetts, who had overseen the fort's construction.

[4] The Sebasticook and Kennebec rivers provided major early routes to transport food, goods, and more settlers.

Benedict Arnold followed the Kennebec River north in 1775, stopping at Fort Halifax in Winslow on his ill-fated attempt to invade Canada.

The Fort Halifax blockhouse, the nation's oldest wooden structure of its type, was rebuilt after the original was swept down the Kennebec River by raging flood waters on April 1, 1987.

Thousands of Irish and French Canadian immigrants used the Old Canada Road (now a scenic byway) section of U.S. Route 201 during the 19th century to find seasonal or project employment, and later made the Kennebec River Valley region their home.

Modern Winslow developed around the Hollingsworth & Whitney Company paper mill, located along the Kennebec River.

Today, Winslow is a bedroom community for some middle- and upper-middle-class families who work in nearby Waterville and Augusta.

The town was home to the state's largest July 4 fireworks display until it moved to Clinton, Maine in 2016.

It borders the towns of Benton to the north, Albion to the east, China to the southeast, Vassalboro to the south, and (across the Kennebec River) Waterville to the west.

[11] Major employers in Winslow include Mid-State Machine Products, Lohmann Animal Health International, Orion Rope Works, and Northeast Laboratories.

A second renovation project, adding a junior high wing and band room, plus expanding a gym and cafeteria was completed in 2020.

The middle school used to house grades 6–8 at 6 Danielson Street until 2020 when it closed due to an aging and an unreliable building.