What colonies had slaves?

Slavery in the United States developed over time and from place to place. It is a common misconception that slavery was a uniquely Southern institution. In fact, slavery was initially legal in all thirteen colonies, and it wouldn't be until after the American Revolution that a growing number of individuals began to question how the existence of slavery could be reconciled with the principle of liberty on which the Revolution had been fought.
Prior to the Revolution, all of the American colonies had slaves. Although the slave population was higher in the South, there were still pockets in the North where slaves formed a substantial proportion of the labor force. In Boston, for instance, some 20–25% of the population consisted of slave laborers. Nevertheless, it was the Northern states that embarked upon the gradual abolition of slavery in their territories.
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