Slaveowners kept workers in bondage by forcing them to sign long indenture contracts (40 to 99 years) or threatening to sell them elsewhere. The U.S. government-run salt works, Illinois Salines, was one of the largest businesses in the Illinois Territory; the government hired thousands of slaves from slaveholders in slave states to keep the salt brine kettles boiling continuously. However, Freed black people could be kidnapped and sold in St. Louis (or any other slave state) where it was legal.
To better understand how recent these events were, my 4th great-grandfather, Nero Cooper I (1813–1900) was a private in the Civil War yet he was still the property of Illinois senator, Stephen A. Douglas. Douglas helped pass the Compromise of 1850 (compromised a congressional balance between free and slave states) then lost the 1860 presidential election to Republican Abraham Lincoln. Douglas designated Chicago the northern terminus of the Illinois Central Railroad and worked on a transcontinental route. Less than 4 generations ago, Illinois founding fathers sold goods to plantations, bought cotton grown by enslaved persons, and then deposited the profits into the Illinois State Treasury. That money funds your treasury paycheck today.