Despite the pleas of land speculators, Congress would not budge on opening the Northwest Territory to slavery. Neither would Congress stir itself to pass laws seizing and freeing slaves already present. The territorial legislatures did not have the power to introduce it, so far as this non-lawyer can tell. They owed their existence to the same law which prohibited it and could not violate their own organic laws. They might, however, have the power to throw it out.
While slaveholders did not flood into Illinois in a great deluge, creating a South Carolina on the Mississippi, the ambiguity of the situation created enough of a window for the more adventurous ones to come just as they came to similar terrain and climes just across the Ohio and Mississippi. The census found them and their human property in 1800 and every ten years thereafter through 1840.
The owners of 107 slaves took the chance on Illinois before it had a territorial legislature. Their slaves amounted to 4.25% of the total population, right between New York’s 3.52% and New Jersey’s 5.88% in the same census. From that, one might conclude that Illinois had an embryonic, but healthy slave society. Maybe some sections of the state did, but a decade more brought only 61 more slaves into the territory. The small numbers made that into a 63.69% increase, but at the same time the free black population came in at more than eight times the previous total. The white population, not limited by the heavy social and legal constraints placed on all black people, grew even faster.
But then 1820 shows the slave population ballooning out to 917. The greater increase in the white population meant that they constituted a smaller proportion of the states’ totals, but in just a decade Illinois blacks went from 78.49% free to 66.74% enslaved. What happened?
Popular sovereignty, not yet called that and never explicitly adopted, rode into the gap left by Congressional indifference. The slaveholders willing to risk Illinois wanted some security and the legislature gave it in the form of an apprenticeship system that amounted to slavery in all but name. The legislature followed the example of Ohio and Indiana in passing laws that forbade the immigration of free blacks. In December, 1813, the territory gave free blacks fifteen days’ notice to vacate the state or suffer 39 lashes. Other laws required them to hold certificates proving their freedom. Unfortunates who did not register and get their certificate, and have it on them when stopped, the law declared runaways. The sheriff would hold them and advertise their presence. If no owner appeared, the “runaway” would go on up for auction as an indentured servant for a year.
So far as slaves went, the territory permitted non-residents to rent their slaves out to residents in Illinois for up to a year without the slave receiving freedom at the end of the term. This the territory justified under the claim that, among other things, white men could not make salt. It amounted to virtually open importation of slaves, so long as a resident could find a convenient slaveholder with a few to spare and, if necessary, a willingness to rotate them out of the territory every year or so.
Statehood came in 1818, with the apprentice system of slave codes in place. Illinois outlawed slavery in its constitution and kept right on practicing it with the serial numbers filed off. That year freed the state from the Northwest Ordinance for good and soon after the Missouri Compromise opened that state to slavery, making Illinois a stop on the road to slavery’s new west. Some Illinoisans wished that more would stay and settle their own state. More wished they could get in on the riches that slavery brought to Missouri and so a movement grew to establish slavery outright and openly in the Land of Lincoln.