Few reliable statistics exist on the number of fugitive slaves that reached the British North American Provinces prior to the Civil War. Biased under enumeration troubled the 1851 and 1861 Canadian census data. Both the abolitionist and proslavery presses frequently distorted their estimates of the size of the fugitive slave population. But certainly the trickle of fugitive slaves that regularly reached Canada after the War of 1812 turned into a torrent after the passage of the Fugitive Slave Law of 1850.

The vast majority of these fugitive slaves settled in Canada West. By 1860 thirtly thousand fugitives had apparently settled in the province; they represented three-fourths of the black population there. Although the number of blacks in the total Canadian population probably never exceeded sixty-two thousand (about 2.5 percent) before the Civil War, black numbers may have appeared larger as a result of heavy concentrations in certain Canada West communities, particularly Chatham (20 percent), Amherstberg (25 percent), and Colchester (33 percent).

Source:
The Black Abolitionist Papers: Volume II, University of North Caronina Press Chapel Hill and London, 1986, pp. 143