William Robertson was born on 29 March 1747, in Dunfermline, Fife, Scotland, United Kingdom. He married Janet Wallace about 1769, in Dunfermline, Fife, Scotland, United Kingdom. They were the parents of at least 7 sons and 3 daughters.
Scottish and English: patronymic from the Middle English, Norman French, and Older Scots personal name Robert + -son. This surname is especially common in Scotland, where Robert was a popular personal name and the name of three kings of Scotland, including Robert the Bruce (1274–1329).
Americanized form (and a rare Swedish variant) of Swedish Robertsson: patronymic from the personal name Robert .
Americanized form of Norwegian and Danish Robertsen, a cognate of 1 above.