The Thorn surname, your father's surname looks to be English per what surnamedb.com says about the name.
Last name: Thorn
This interesting surname with variant spellings Thorne, Thornes and Thorns has two possible origins. Firstly, it is of English locational origin from one of two places called Thorne, either in Somerset or the West Riding of Yorkshire, both recorded as "Torne" in the Domesday Book of 1086. The placenames derive from the Olde English pre 7th Century "thorn" meaning thorn bush. The name may also be topographical for a "dweller by the thorn bush". The surname is first recorded in the early 13th Century (see below). One Hugh Thorne, is registered in the Hundred Rolls of Cambridgeshire (1273), Magge de Thornes, is noted in the Court Rolls of the Manor of Wakefield, Yorkshire (1275). Recordings of the surname from the London Church Registers include; Margery Thorn, who married William Knyght, on November 24th 1543, at Christchurch, Greyfriars, Newgate; the christening of John, son of John Thorne, on June 2nd 1550, at St. Leonard's, Eastcheap; on July 19th 1551, Thomas Thorne married Julyan Rawsby, at St. Andrew, Enfield; and Barbara Thorne was christened on February 18th 1560, at St. Lawrence Jewry and St. Mary Magdalene, Milk Street. The first recorded spelling of the family name is shown to be that of William Thorn, which was dated 1206, in the "Curia Regis Rolls of Sussex", during the reign of King John, known as "Lackland", 1199 - 1216. Surnames became necessary when governments introduced personal taxation. In England this was known as Poll Tax. Throughout the centuries, surnames in every country have continued to "develop" often leading to astonishing variants of the original spelling.
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