Wrong! The census of 1830 showed 747 slaves in Illinois. (Illinois was admitted into the Union in 1818.)
John Crenshaw's Hickory Hill Plantation and salt-mine was opened in 1842 and operated for six years until the owner was forced to close it due to being seriously injured by a slave with an axe. It was run entirely by black slave labor.
BTW,this is the same time that Old Honest Abe was a member of Congress. He even spent a night or two at the Plantation as late as 1840. He knew Mr. Crenshaw well and one of his Sangamon County law firm partners married one of John Hart Crenshaw's daughters. There can be little doubt that Mr. Lincoln knew all about Illinois slavery.
This is no "slave house story." I've visited the place and seen the chains in the third-floor slave quarters.
The Hickory Hill historical site closed in 1996 due to the ill health of the owner. Negotiations are underway with the State of Illinois to purchase the site as an historic property. It's quite well documented.
BTW, does the census identify people as "slaves" or "other than white"?
You do know American Indians who were independent of tribes as well as Gypsies (Roma), Jews and Sa'ami were so identified.