Origin uncertain. There is some evidence that it may be an altered
form of an English patronymic, Cittison, from an unidentified
personal name. Alternatively, it may be an ornamental adoption of the
vocabulary word citizen as a surname by people with republican
beliefs, in some cases representing an Americanized form of the French
equivalent citoyen.
Dictionary of American Family Names, Oxford University Press, ISBN 0-19-508137-4