La Harpe is a city in Hancock County, Illinois, United States. The population was 1,235 at the 2010 census, down from 1,385 at the 2000 census.
La Harpe is located in northeastern Hancock County at 40°34′59″N 90°58′08″W / 40.582925°N 90.968770°W / 40.582925; -90.968770, south of the South Branch La Moine River. Illinois Route 9 passes through the city as its Main Street, leading east 25 miles (40 km) to Bushnell and west 13 miles (21 km) to Dallas City on the Mississippi River. Illinois Route 94 intersects IL 9 at the western edge of the city, and leads north 15 miles (24 km) to Stronghurst.
According to the 2010 census, La Harpe has a total area of 1.36 square miles (3.52 km), all land.
As of the census of 2000, there were 1,385 people, 561 households, and 383 families residing in the city. The population density was 1,021.8 people per square mile (393.2/km²). There were 604 housing units at an average density of 445.6 per square mile (171.5/km²). The racial makeup of the city was 99.78% White, 0.07% from other races, and 0.14% from two or more races. Hispanic or Latino of any race were 0.14% of the population.
There were 561 households out of which 31.2% had children under the age of 18 living with them, 57.0% were married couples living together, 9.4% had a female householder with no husband present, and 31.6% were non-families. 29.1% of all households were made up of individuals and 16.0% had someone living alone who was 65 years of age or older. The average household size was 2.39 and the average family size was 2.93.
In the city, the population was spread out with 24.0% under the age of 18, 6.5% from 18 to 24, 24.4% from 25 to 44, 23.5% from 45 to 64, and 21.7% who were 65 years of age or older. The median age was 41 years. For every 100 females, there were 85.2 males. For every 100 females age 18 and over, there were 77.3 males.
The median income for a household in the city was $32,589, and the median income for a family was $37,708. Males had a median income of $31,250 versus $20,400 for females. The per capita income for the city was $15,586. About 4.6% of families and 7.4% of the population were below the poverty line, including 8.9% of those under age 18 and 6.3% of those age 65 or over.