| State | Name | Sponsored by |
| Alabama | Encyclopedia of Alabama | Alabama Humanities Foundation |
| Arkansas | Encyclopedia of Arkansas | Central Arkansas Library System |
| Colorado | Colorado Encyclopedia | History Colorado |
| Connecticut | Encyclopedia of Connecticut Biography (10 vols, 1917–23) | American Historical Association |
| Connecticut | Connecticut History | CThumanities |
| Florida | Floripedia: A Florida Encyclopedia (a collection of links to original sources, not an encyclopedia) | Florida Center for Instructional Technology, University of South Florida |
| Georgia | New Georgia Encyclopedia | Georgia Humanities and the University of Georgia Press |
| Illinois | Encyclopedia of Chicago | Chicago History Museum |
| Indiana | Encyclopedia of Indianapolis | Indianapolis Public Library |
| Kansas | Kansapedia (not to be confused with KansasPedia.com) | Kansas Historical Society (a state agency) |
| Kentucky | The Kentucky Enciclopedia | University Press of Kentucky |
| Kentucky | Encyclopedia of Louisville | University Press of Kentucky |
| Louisiana | 64 Parishes (formerly Know Louisiana) | Louisiana Endowment for the Humanities |
| Maine | Maine: An Encyclopedia | Publius Research |
| Massachusetts | Encyclopedia of Massachusetts, biographical—genealogical (1916) | |
| Minnesota | MNopedia | Minnesota Historical Society |
| Mississippi | Mississippi Encyclopedia | Mississippi Humanities Council |
| Missouri | Missouri Encyclopedia | State Historical Society of Missouri |
| Nevada | Online Nevada Encyclopedia | Nevada Humanities |
| New York | Encyclopedia of New York State | Not free; requires subscription. Available through Gale. 30-day free trial from booklibrarian.com. |
| North Carolina | NCPedia | State Library of North Carolina |
| Ohio | Ohio History Central (archived location) | Ohio History Connection |
| Oklahoma | The Encyclopedia of Oklahoma History and Culture | Oklahoma Historical Society |
| Oregon | The Oregon Encyclopedia | Portland State University and the Oregon Historical Society |
| Pennsylvania | Encyclopedia of Greater Philadelphia | Mid-Atlantic Regional Center for the Humanities |
| South Carolina | South Carolina Encyclopedia | "A joint project of South Carolina Humanities, the University of South Carolina Press, the USC Libraries, the USC Center for Digital Humanities, the USC College of Arts & Sciences, the USC Institute for Southern Studies, the South Carolina State Library, and many other organizations." |
| Tennessee | Tennessee Encyclopedia | Tennessee Historical Society – University of Tennessee Press |
| Texas | Handbook of Texas | Texas State Historical Association |
| Virginia | Encyclopedia Virginia | Virginia Foundation for the Humanities and Library of Virginia (formerly the Virginia State Library) |
| Virginia | Encyclopedia of Virginia Biography (1915-) | Robarts Library, University of Toronto. Arranged by time period and office held, not alphabetically. |
| Washington | HistoryLink | HistoryLink, 4Culture, King County, Washington, Seattle Office of Arts & Culture, The Norcliffe Foundation |
| West Virginia | e-WV: The West Virginia Encyclopedia | West Virginia Humanities Council |
| Wyoming | Encyclopedia of Wyoming | Wyoming State Historical Society |
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