On Thursday, August 12, 2021, the U.S. Census Bureau released initial 2020 Census results showing local population shifts along with racial and ethnic diversity changes. This information was released in the "legacy" format, with more user-friendly data expected to be released by September 30, 2021.
A press release from the U.S. Census Bureau about the data is available via this link.
Population counts for counties are accessible via the U.S. Census Bureau's Quick Facts website. To view data for your county, enter your county's name in the field at the top left-hand side of the page.
Illinois' legacy format data is available via this link.
Information about how "legacy" data can be used is available on the Decennial Census P.L. 94-171 Redistricting Data page.