U.S. Census Bureau provides a wealth of information on demographics in the United States, searchable by geography (country, state, community) as well asspecific measurements (population, income, etc.) 

Office of Strategic Research in the Ohio Department of Development offers its own census information, as well as county profiles for all Ohio counties.  It also provides “Research Links” that touch on nearly all measurable sectors of society.

The Ohio State University Extension Data Center provides “current, relevant demographic, economic, and agricultural data for Ohio,” via an interactive set of county-specific data and a number of  reports, as well as a number of related links.