@ GlassAxe- The history of slavery in the North is well documented through census counts and various colonial and state slave codes. Many states including Pennsylvania, Maryland, Delaware, and Connecticut had laws governing how slaves were treated as well as their rights. There were also laws on the books that stated harsh penalties for free black men that allowed whites to make them slaves, or indentured servants as they were so politely called during the time. This could be the punishment for any free black who was caught harboring an escaped slave and could not pay the lofty fine for doing so.
Pennsylvania might be of particular interest to you. The state had a number of reported slaves, and some of the most common slave owners were the Quakers, Dutch and Swedes that had settled the region. The state of Pennsylvania did not actually emancipate slaves until 1948, even though the Pennsylvania emancipation law was passed in 1820. This gave slave owners 28 years of hard labor to recoup the investment made in raising these "people". As you assumed, the North is just as responsible for facilitating slavery as the south. The only reason slavery did not catch hold in the North as it did in the south was because it was cheaper to pay the Irish and Scottish immigrants coming off the docks than it was to buy and maintain slaves.