In 1860 Illinois had only 7,628 blacks out of a population of 1.7 million. These persons were either the descendants of the tiny number of blacks who already lived in Illinois prior to the adoption of an outright prohibition in the 1840's or those few who had managed to escape detection despite the law.
And the other northern states as well.
Nobody denies that there were some free blacks in other northern states. The majority, however, remained in the south. One of the major reasons for this was an outright prohibition against blacks from entering several of the northern states. Illinois had this prohibition as did most of the midwestern states along the north-south border. Oregon even wrote it into their state constitution.
I thought the largest number of free blacks was in Louisiana.
Louisiana had about 20,000 persons officially listed as free blacks in 1860, though the numbers for that state are unreliable from year to year. In addition to free blacks Louisiana had three additional categories in which they classified their demographics - a holdover from their unique Spanish-French history. They also had mulattos (1 black parent), quadroons (1 black grandparent), and octoroons (1 black great grandparent). Most other states would count mulattos and possibly quadroons in their "free black" count.
Of states with reliable free black counts, Maryland had the most in 1860 with 83K. Virginia was second with 58K, then Pennsylvania with 56K.
While laws preventing black residents had an impact the reason most blacks remained in the South was family and familiarity.
Lousiana's classification methods may account for the statement I saw about its pre=eminance wrt Free Blacks. Had they used Virginia's would that have made it #1?
I've posted previously the dozens of terms the Spanish used to locate people genealogically in the racial-composition spectrum. They included persons of mixed ancestry descended from Indians as well as blacks and Europeans, and included such terms familiar from American geography and history (shorn of most of their meaning) as chino, cholo, zambo, lobo, ladino, coyote, marron, cimarron, and negro fino (the last being a person 3/4 African, 1/4 European, what English speakers called "griff", from "griffin", a term used in India, however, to mean Englishmen new to the country), as well as more exotic combinations like cambur, cambujo, chamizo, pardo, cuatrero, and torna atras. Some of the terms are synonyms: zambo is a synonym for negro fino (although the definition of zambo was different in South America); and what Louisianians called "octoroon" was called in Spanish albino, ochavado, or quinteron. There were also two words for persons who were 1/16th black, who would have been called "statutory whites" in the British West Indies: requinteron and salta atras.
This Spanish terminology would have been recorded on baptismal or birth certificates and served to locate the person in society.