Data is taken from: https://web.viu.ca/davies/H320/population.colonies.htm , https://userpages.umbc.edu/~bouton/History407/SlaveStats.htm , and http://www.thomaslegion.net/totalslaveslaverypopulationinunitedstates17901860bystate.html .
Colonized borders based on https://digital.newberry.org/ahcb/index.html (the Atlas of Historical County Boundaries). Created in QGIS.
This data sometimes list slaves in areas where slavery had been explicitly made illegal (the area of the Northwest Territory especially). The numbers are quite small and I don’t know if they indicate an error by the census takers, or if some people were living with their slaves beyond the reach of the law.