Thomas McKean (1734–1817) began his law career in Delaware and in 1777 became chief justice of Pennsylvania, serving until 1799 when he was elected governor of Pennsylvania. In 1790 he lived on the east side of Third Street (HEADS OF FAMILIES, PA. description begins Heads of Families at the First Census of the United States Taken in the Year 1790: Pennsylvania. 1908. Reprint. Baltimore, 1970. description ends , 238).