Henry is a city in Marshall County, Illinois, United States. The population was 2,320 at the 2020 census. It is part of the Peoria Metropolitan Statistical Area.
Henry is named after General James D. Henry and was initially surveyed in 1834. The topography of the land on the west side of the Illinois River, with relatively steep banks rising well above river level, assured early settlers that their homes would not flood.
Its slogan, "Best Town in Illinois by a Dam Site", is derived from the city's distinction of having the first lock and dam built on the Illinois River. It was completed in 1870 at a cost of $400,000.
The retreat house of the Roman Catholic Diocese of Peoria (Nazareth Retreat House, formerly King's House) is located here.
Henry is located in northern Marshall County at (41.113152, -89.360218). It is bordered to the east by the Illinois River, which forms the boundary with Putnam County.