Slavery in Illinois existed for more than a century. Illinois did not become a state until 1818, but earlier regional systems of government had already established slavery. France introduced African slavery to the Illinois Country in the early eighteenth century. French inhabitants of Illinois continued the practice of owning slaves throughout the Illinois Country's period of British rule (1763), as well as after its transfer to the new United States in 1783 (See, Illinois County, Virginia). The Northwest Ordinance (1787) banned slavery in Illinois and the rest of the Northwest Territory. Nonetheless, slavery remained a contentious issue, through the period when Illinois was part of the Indiana Territory and the Illinois Territory and some slaves remained in bondage even after statehood until their gradual emancipation by the Illinois Supreme Court.
During the early decades of statehood, the number of slaves in Illinois dwindled. Nevertheless, in the decade before the American Civil War an anti-Black law was adopted in the state, which made it difficult for new Black emigrants to enter or live in Illinois. Near the close of the civil war, Illinois repealed that law and became the first state to ratify the Thirteenth Amendment to the Constitution of the United States, which abolished slavery nationally.
During the French colonial period of Illinois, Illinois was a part of the region known as the " Illinois Country", which also loosely encompassed lands that would become the future U.S. states of Indiana, Wisconsin, and Missouri was part of New France and, as such, was governed by its slavery laws. French settlers first brought African slaves into the Illinois Country from Saint-Domingue now the present-day country of Haiti around 1720 under the legal terms of the Code Noir, which defined the conditions of slavery in the French Empire and restricted the activities of free Negro people.   The first documented African slavery in Illinois was in 1721, when Philip François Renault imported five hundred negro slaves to the Illinois Country. After an unsuccessful attempt at lead mining, Renault founded St. Philippe, Illinois, in 1723, and used his slaves for agricultural purposes to produce crops.
The institution of slavery continued after Britain acquired the Illinois Country in 1763 following the French and Indian War. At the time, nine hundred slaves lived in the territory, although the French would take at least three hundred with them as they left the state for lands west of the Mississippi River. 
Slavery continued following the American Revolutionary War, when the territory was ceded to the United States. The first legislation against slavery was the Northwest Ordinance of 1787, which forbade slavery in the Northwest Territory. However, territorial laws and practices allowed human bondage to continue in various forms. Territorial governors Arthur St. Clair and Charles Willing Byrd supported slavery and did not enforce the ordinance. When the Indiana Territory was split from the Northwest Territory in 1800, residents petitioned the United States Senate to allow slaves. A proposal offered emancipation to Illinois-born male slaves at age thirty-one and female slaves at age twenty-eight. Southern-born slaves were to be slaves for life. No response to the proposal was ever issued. 
Illinois Territory continued the Indiana Territory Black Code which restricted free blacks, who had to prove they were free.  Also, slaveowners could force their slaves to sign indentures of very long length (40 to 99 years), threatening them with sale elsewhere if they refused. Furthermore, free blacks could be kidnapped and sold in St. Louis in Missouri Territory or states where such sales were legal.  Also, salt was necessary for preserving meat, and the Illinois Salines, a U.S. government-run salt works near Shawneetown was one of the largest businesses in the Illinois Territory, exploiting between 1,000 and 2,000 slaves hired out from masters in slave states to keep the salt brine kettles continuously boiling.
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While Illinois' first state constitution in 1818 stated that slavery shall not be "thereafter introduced", slavery was still tolerated in the early years of Illinois statehood, and the constitution did not have a clause forbidding its amendment to allow slavery. However, due to the efforts of a coalition of religious leaders ( Morris Birkbeck, Peter Cartwright, James Lemen, and John Mason Peck), publisher Hooper Warren and politicians (especially Edward Coles, Daniel Pope Cook and Risdon Moore), Illinois voters in 1824 rejected a proposal for a new constitutional convention that could have made slavery legal outright.  Slavecatchers from Missouri would travel to Illinois either to recapture escaped slaves, or kidnap free blacks for sale into slavery, particularly since Illinois' legislature tightened the Black Code to state that recaptured escaped slaves would have time added to their indentures, and the following year barred blacks from being witnesses in court cases against whites, then two years later barred blacks from suing for their freedom. In Phoebe v Jay, Judge Samuel D. Lockwood, previously Coles' anti-convention and abolitionist ally, held that the 40 year indenture of Phoebe (entered into in 1814) could be transferred to Joseph Jay's heir, his son William Jay, arguing that the new state's Constitution superceded the anti-slavery provisions of the Northwest Ordinance.  Nonetheless, in a series of legal decisions beginning with Cornelius v. Cohen in 1825, the Illinois Supreme Court gradually developed a jurisprudence to gradually emancipate slaves in Illinois. In that first case, the justices decided that both parties must be in agreement and sign a servitude contract. In Choisser v. Hargrave, the court decided that indentures would not be enforced unless they complied with all provisions of Illinois law, including that they be registered within 30 days of entering the state. In 1836, the court in Boon v. Juliet held that children of registered slaves brought into the state were free, and could themselves only be indentured until the age of 18 or 21 years (depending on their sex) according to the state's Constitution. In Sarah v. Borders (1843), the court held that if any fraud occurred in the signing of an indenture contract, it was void. Finally, in the 1845 decision, Jarrot v. Jarrot, that same court ended tolerance of slavery even for descendants of former French slaves, holding that descendants of slaves born after the 1787 Northwest Ordinance were born free. 
In one of the predecessors of the Dred Scott decision, Moore v. People, 55 U.S. 13 (1852),  the U.S. Supreme Court upheld a conviction for harboring a fugitive slave from Missouri, as had the Illinois Supreme Court a few years earlier. Illinois residents participated in the underground railroad for fugitive slaves seeking freedom, with major routes beginning in the Mississippi River towns of Chester, Alton and Quincy, to Chicago, and lesser routes from Cairo to Springfield, Illinois or up the banks of the Wabash River. 
The Illinois' Constitution of 1848 specifically banned slavery, section 16 of its Declaration of Rights specifying, "There shall be neither slavery nor involuntary servitude in the State, except as a punishment for crime whereof the party shall have been duly convicted." Nevertheless, subsequent legislation led to one of the most restrictive Black Code systems in the nation until the American Civil War. The Illinois Black Code of 1853 prohibited any Black persons from outside of the state from staying in the state for more than ten days, subjecting Black emigrants who remain beyond the ten days to arrest, detention, a $50 fine, or deportation. The Code was repealed in early 1865, the same year that the Civil War ended.  At that time, Illinois also became the first state to ratify the Thirteenth Amendment to the United States Constitution, which abolished slavery nationally. 
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