Hamersley was born in Great Haseley, Oxfordshire, the son of Hugh Hamersley JP, DL (1813–1884) and Mary Anne Phillpa ( Edwards; died 1877). Initially living at Haseley House, Great Haseley, he moved to Church Manor House, Pyrton, Oxford prior to 1861 where his father had inherited the manor that had been in the family since 1781. Alfred was not to inherit the manor. Rather, it passed to his younger brother Edward Samuel in 1884 at which time Alfred was living in New Zealand. Pyrton manor did not revert to the older line of Alfred, but rather in 1909, Edward's widow gave the manor to the son of her husband's sister, Major Hugh C.C. Ducat, who took the name Ducat Hamersley and whose son, Colonel Hugh Ducat Hamersley, inherited in 1945. In the Pyrton parish church are a number of monuments in the nave mostly to members of the Hamersley family. One of these is a brass tablet, designed by Eric Gill, to Col. Alfred St. George Hamersley, M.P.
