As to the number of negroes in Pennsylvania at different times during the colonial period almost any estimate is at best conjecture. Not only are there few official reports, but these reports, in the absence of any definite census, are of little value.[39] Apparently one of the best estimates was that made in 1721, which stated the number of blacks at anywhere between 2,500 and 5,000.[40] In 1751 it was at least widely believed that there were in Philadelphia 6,000, and it is asserted that the total number in Pennsylvania including the Lower Counties was 11,000.[41] It is probable that the same number was not much exceeded in Pennsylvania proper at any time before 1790. In these estimates no attempt was made to distinguish the free from the slaves. The number of slaves, it is true, was very near the total at both these periods, but after the middle of the century it began dwindling as the number of negro servants and free men increased. In 1780 a careful estimate placed the slaves at 6,000.[42] According to the Federal census of 1790 the number of negroes in Pennsylvania was 10,274.[43]
Of these negroes the great majority throughout the slavery period were located in the southeastern part of Pennsylvania, in and around Philadelphia. There were many in Bucks, Chester, Lancaster, Montgomery, and York counties. There were negroes near the site of Columbia by 1726. John Harris had slaves by the Susquehanna as early as 1733. In 1759 Hugh Mercer wrote from the vicinity of Pittsburg asking for two negro girls and a boy. The tax-lists and local accounts reveal their presence in many other places.[44] Doubtless a few might be traced wherever white people settled permanently. In general it may be said that they were owned in the English, Welsh, and Scotch-Irish communities. The Germans as a rule held no slaves.
Where negroes were owned they were for the most part evenly distributed, there being few large holdings. In rare instances a considerable number is recorded as belonging to one man, and the iron-masters generally had several. The tax-lists, however, indicate that the average holding was one or two, except in Philadelphia among the wealthier classes where it was double that number.[45]