[B]Free blacks were fairly common in the antebellum South, constituting 8 percent of southern blacks in 1840. Most had gained their freedom through manumission (especially common just after the Revolutionary War) or had been born free to a free mother. Slaves who'd been permitted to earn money in their spare time sometimes made enough to buy their freedom. Another route was being bought and freed by free relatives or friends. But some who bought slaves in this way didn't formally free them for years, partly because freedmen paid higher taxes than slaves or whites. Courts since colonial times had recognized the right of free blacks to own slaves. This gave rise to an odd arrangement in which people lived as free but were legally someone else's property. This was benevolent slavery.
Between 1800 and 1830, slave states began restricting manumission, seeing free blacks as potential fomenters of slave rebellion. Now you could buy your friends, but you couldn't free them unless they left the state -- which for the freed slave could mean leaving behind family still in bondage. So more free blacks took to owning slaves benevolently. Being a nominal slave was risky -- among other things, you could be seized as payment for your nominal owner's debts. But at least one state, South Carolina, granted nominal slaves certain rights, including the right to buy slaves of their own.
Nobody's sure how many such arrangements existed. A widely cited but imperfect source is the 1830 federal census, chosen because it supposedly represents the high point of black slave ownership. One count, taking the data at face value, found 3,777 free black heads of household who had slaves living with them. If that's accurate, about 2 percent of southern free blacks owned slaves.[/