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Do you have this, it gives his date of birth as around 1775. From Sarum Marriage Licence Bonds.
SAMUEL MILLARD
Birth year 1775
Bond day 31 Jan 1797
Marriage year 1797
BRISTOL ST THOMAS
Groom: Samuel Millard aged 22, batchelor
Occupation tallowchandler
Groom's parish Bristol St Thomas, Somerset
Bride: Ann Vines
Bride's age 23
Bride's marital status spinster
Bride's parish Brinkworth (Grittenham) Wiltshire
Bondsman 1 Jacob VINES ,dairyman, Grittenham, Brinkwth