County Profiles which highlight key characteristics of counties in the United States can be found at any of the following websites:
United States Census Bureau
Census Bureau - A-Z subject list of Census information.
American Fact Finder
American Fact finder provides social, demographic, housing, and economic data for varying geographic levels taken from various other Census products.
Data USA puts public data in your hands. Instead of searching through multiple data sources that are often incomplete and difficult to access, you can use this source to answer your questions. It allows millions of people to conduct their own analyses and create their own stories about America.
Headwaters Economics Economic Profile System allows you to download socioeconomic reports of communities, counties, and states, including aggregations and comparisons. The Economic Profile System (EPS) uses federal data sources, including the Bureaus of Economic Analysis, Census, and others.
STATS Indiana is the statistical data utility for the State of Indiana, developed and maintained since 1985 by the Indiana Business Research Center at Indiana University's Kelley School of Business. While this site does focus on information specific to Indiana, there is a database that allows you to compares your county to another, in Illinois or anywhere in the country.