| Description: | McHenry County, located in northeastern Illinois, covers an area of 604 square miles and had a 2003 population of 286,091, according to estimates by the U.S. Department of Commerce's Bureau of the Census. Using these figures, McHenry County was the 56th largest county in Illinois geographically, but 7th largest in terms of population. Combining these two measures, McHenry County had the 7th highest population density per square mile among Illinois 102 counties. | |