Aledo (u--doh) is a city in Mercer County, Illinois, United States. The population was 3,640 at the 2010 census, up from 3,613 in 2000. It is the county seat of Mercer County. History Aledo was established in the 1850s when the railroad was extended to that point. It was briefly named DeSoto, after Hernando de Soto, until the discovery of an identically named village in Jackson County, Illinois. Development in the Downtown Aledo Historic District began in the 1850s, and the oldest surviving buildings date from the following decade. A post office has been in operation at Aledo since September 24, 1856. In 1857, the county seat was moved to Aledo from Millersburg after a countywide referendum. Aledo was incorporated on August 15, 1863. In the 1950s, the first Tastee-Freez in the United States was built in the downtown. Geography Aledo is located at (41.200172, -90.749956). According to the 2010 census, Aledo has a total area of , of which (or 99.5%) is land and (or 0.5%) is water. Climate Demographics As of the census of 2010, there were 3,640 people, 1,568 households, and 947 families residing in the city. The racial makeup of the city was 98.5% (3,586) white; 0.6% (22) African American; 0.0% (1) Native American; 0.3% (12) Asian; 0.1% (4) from other races; and 0.4% (15) from two or more races. Hispanic or Latino of any race were 1.2% (45) of the population. There were 1,568 households, out of which 24.5% had children under the age of 18 living in them, 49.0% were married couples living together, 3.6% had a male householder with no wife present, 7.8% had a female householder with no husband present, and 39.6% were non-families. 35.7% of all households were made up of individuals, and 20.2% had someone living alone who was 65 years of age or older. The average household size was 2.20 and the average family size was 2.84. The male population made up 47.5% (1,728), the female population made up 52.5% (1,912). There was 6.3% (229) of the population under 5 years; 17.1% (622) from 5 to 19 years; 10.3% (374) from 20 to 29 years; 10.2% (368) from 30 to 39; 12.5% (453) from 40 to 49; 12.9% (472) from 50 to 59; 12.1% (441) from 60 to 69; 8.2% (296) from 70 to 79; and 10.6% (385) were 80 years and over. The median age was 45.8 years.