golux: "The last slaves were freed in the North."
By the time the 13th Amendment was ratified, in December 1865, all but a relative handful of slaves in Kentucky, Delaware & New Jersey had already been freed -- either by their own states, by the Emancipation Proclamation or by just walking away.
Of New Jersey's 1860 18 remaining old "grandfathered" slaves, 16 are said to have still been alive to be freed by the 13th Amendment.
We are not told who those 16 were, but personal body-servants seems likely, meaning their de-facto status would not change much until either they or their now "employers" died.
Leaving the question regarding Delaware (~1,800 slaves) & Kentucky (maybe 50,000 remaining slaves): were they "North" or "South"?
Well, before the Civil War, as slave-states they were considered "South".
During the war they remained in the Union, but provided large numbers of troops to the Confederacy -- they were Southern Union states.
After the Civil War Kentucky & Delaware nearly always voted solidly with Democrats of the Solid South.
Today, are Kentucky & Delaware more "North" or "South"?
Well, when a Delaware Democrat politician like Joe Bye-Done says, "they're going to put y'all back in chains", he sounds pretty Southern to me.
Kentucky seems pretty much of mixed minds -- Northern style Democrats can still win statewide elections there, though not always.
On the question of who, actually, did clear & plow the land, then plant & pick cotton -- my guess is a large percentage of that work was done by yeomen farmer families of modest means.
But the lure of profitable plantation life was so great that as soon as a white family got good at farming, dad would visit the local bank to borrow enough money to set them up as "planters", and so let others do the hardest work for them.