Deep River is a town in Middlesex County, Connecticut, United States.

The town is part of the Lower Connecticut River Valley Planning Region.

[2] The town center is designated by the U.S. Census Bureau as a census-designated place (CDP).

The portion of the original colony east of the Connecticut River was set off as a separate town in 1665.

The site of the present village of Deep River was said to have been owned by John, Nathaniel, and Philip Kirtland in 1723.

[4][5] Saybrook Colony, along the mouth of the Connecticut River, was one of the early settlements in the area.

[6] The rival Comstock, Cheney & Company was established in nearby Ivoryton in the 1860s.

These sites in town are on the National Register of Historic Places: Every year on the third Saturday in July, Deep River hosts the Deep River Ancient Muster, the largest one day gathering of fife and drum corps in the United States.

As of the census of 2000, there were 2,470 people, 1,023 households, and 652 families living in the Deep River Center CDP.

The towns of Deep River, Chester, and Essex make up Regional School District #4.

Additionally, the Connecticut Transition Academy at Mount Saint John which serves students for grades from elementary to high school which is located on Kirtland Street and across the river from Gillette Castle State Park, respectively.

Services include connections to the Old Saybrook Train Station, served by Amtrak and Shoreline East railroads.