Keithsburg is a city in Mercer County, Illinois, United States on the Mississippi River. The population was 609 at the 2010 census, down from 714 in 2000. It was named for Robert Keith, a pioneer settler.
Keithsburg is located at 41°6′0″N 90°56′14″W (41.100020, -90.937293).
According to the 2010 census, Keithsburg has a total area of 3.181 square miles (8.24 km2), of which 2.56 square miles (6.63 km2) (or 80.48%) is land and 0.621 square miles (1.61 km2) (or 19.52%) is water.
The Keithsburg Division of the Mark Twain National Wildlife Refuge Complex lies north of Keithsburg.
As of the census of 2000, there were 714 people, 278 households, and 199 families residing in the city. The population density was 276.9 people per square mile (106.9/km2). There were 306 housing units at an average density of 118.7 per square mile (45.8/km2). The racial makeup of the city was 98.32% White, 0.28% Native American, and 1.40% from two or more races. Hispanic or Latino of any race were 0.42% of the population.
There were 2780 households, out of which 30.2% had children under the age of 18 living with them, 57.2% were married couples living together, 10.1% had a female householder with no husband present, and 28.1% were non-families. 24.5% of all households were made up of individuals, and 16.9% had someone living alone who was 65 years of age or older.