History of Manchester
According to Oxford University Press, Manchester derived its name from Mamucium, the Roman name for the 1st century-settlement and fort. Mamucium itself is a Latinised form of the Celtic meaning "breast-shaped hill".
County of Manchester
The county was named by Algernon Keith-Falconer, 9th Earl of Kintore, the Governor of South Australia after his father-in-law, George Montagu, 6th Duke of Manchester.