Just over one-half of the town's area is covered by Bear Brook State Park.

[5][6] Most of the town's earliest settlement occurred in the eastern part of town along Deerfield Road, around the area now mostly occupied by Bear Brook State Park, and where the Old Allenstown Meeting House is located.

The Suncook Valley Railroad would follow in 1869, which ran northeast along the river, first to Pittsfield and later, to Center Barnstead.

It crossed the Suncook Valley track adjacent to the Catholic Church on Main Street; the Blodgett depot was built at that location to facilitate transfers between the steam road and the interurban.

[9] At this time, a large number of French Canadians, mostly from Quebec, began emigrating to the area to work in the mills.

Eventually, Suncook became one of many New England industrial villages known to locals as "le petit Canada.

More than 10 inches (250 mm) of rainfall caused the Suncook River to overflow, inundating homes, roads, and other low-lying areas.

[1] The highest point in Allenstown is Bear Hill in the southeastern section of town, at 835 feet (255 m) above sea level.

(An additional 3,200 acres (13 km2) of the park are in the neighboring towns of Deerfield, Candia, and Hooksett.