Lacon is a city in, and the county seat of, Marshall County, Illinois, United States. It is part of the Peoria, Illinois Metropolitan Statistical Area. The population was 1,979 at the 2000 census.
Lacon is located at 41°01′26″N 89°24′28″W / 41.023904°N 89.407669°W / 41.023904; -89.407669. It is situated on the east shoreline of the Illinois River. According to the United States Census Bureau, the city has a total area of 1.6 square miles (4.3 km²), of which, 1.6 square miles (4.1 km²) of it is land and 0.04 square miles (0.1 km²) of it (2.42%) is water.
As of the census of 2000, there were 1,979 people, 797 households, and 540 families residing in the city. The population density was 1,233.9 people per square mile (477.6/km²). There were 852 housing units at an average density of 531.2 per square mile (205.6/km²). The racial makeup of the city was 80.09% White, 7.10% African American, 0.10% Native American, 0.20% Asian, 0.10% from other races, and 0.40% from two or more races. Hispanic or Latino of any race were 12.91% of the population.