Actually they were. The legislature of the state of Illinois issued a resolution ( 91_SJ0062) recognizing such:
WHEREAS, The State of Illinois, at the time of its acceptance into the Union in 1818 and for a longtime thereafter, practiced de facto slavery masqueraded as "indentured servitude"; the census of 1840 enumerated slaves in Illinois in violation of the Ordinance of 1787, which outlawed slavery in the Northwest Territories; andWHEREAS, The State of Illinois passed the infamous and unjust Black Laws (1819), otherwise known as the Black Codes, which were a denial of human rights designed to cover up slavery and the slave trade within the borders of the State and
WHEREAS, The State of Illinois supported the Black Codes for more than forty-six years until they were finally repealed; and
WHEREAS, In the State of Illinois the majority of Illinois citizens favored closing the State to African-American residents and withholding the right of citizenship from those African-American residents already living in the State; and
WHEREAS, The State of Illinois passed dehumanizing laws stating that slaves were not persons, but property, and as property the ownership of enslaved Africans was to be fully protected by Illinois law; and
WHEREAS, For many years, Black people, free or otherwise, had no legal status as citizens in the State of Illinois...