This surname is derived from an occupation. 'the tiller,' a tiller of the soil. With Tillyer, cf. Sawyer for Sawer, or lawyer for lower.
1769. Married — John Tillier and Ann Pickernell: St. George, Hanover Square.
1780. — Thomas Roberts and Eleanor Tiller: ibid.
Bardsley, Charles Wareing Endell (1901) A Dictionary of English and Welsh Surnames, with special American instances. London, New York: H. Frowde. Public Domain