According to the census of 1790, about how many enslaved people of african ancestry lived in the colonies?

According to the census of 1790, there were about seven hundred thousand slaves of African ancestry lived in the colonies, (precisely 694,280) with the most living in the state of Virginia where 292,627 enslaved Africans were counted. Although there had been some skepticism about the counting that it might be undercounted. 

the second significant cause of the great migration was the desire of black southerners to escape segregation, known euphemistically as jim crow. rural african american southerners believed that segregation - and racism and prejudice against blacks - was significantly less intense in the north.