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. The day the mayor was supposed to be sworn in he resigned and so the mayor for the next two years is Robert L. Weber. Robert "Bob" Weber served on the City council for many years. He retired a few years ago, but he rejoined the council early this year and is now mayor.