| | Description: | Mercer County, located in northwestern Illinois along the Mississippi River, encompasses a 561 square mile area and had a 2003 population of 17,003, according to estimates by the U.S. Department of Commerce's Bureau of the Census. Using these figures, Mercer County was the 65th largest county in Illinois geographically, but 66th largest in terms of population. Combining these two measures, Mercer County had the 21st smallest population density per square mile among Illinois 102 counties. | |
