He was born about 1802 at Hellingly.
He married Mary Lee (both of Willingdon) after banns, at Willingdon 22 June 1824. The witnesses were Richard Willard and Sarah Lee.
In the 1841 census of Willingdon, Joseph was aged 38, a miller. His wife, Mary, was 41 and his children were Joseph (16), Mary (14), Louisa (12), Frances (11), Emily (10), Eliza (6) and Caroline (2). All were born in Sussex.
In 1845 he became the owner of Polegate Windmill, on the death of his father.
There is mention in a document of a lease of date 14 February 1851 of cottages erected by Joseph Seymour the younger on a piece of land at the seaside in Eastbourne, which Joseph had given up to John Pennington Gorringe.
In the 1851 census of Dunns Farm, Willingdon, he was aged 48, a miller, born at Hellingly, Sussex. His wife, Mary, was aged 50 and born at Elsted. Their children were Frances aged 21, and Eliza aged 16, both born at Willingdon. With them were Hannah Pierce a servant aged 16 born at Jevington and Stephen Seymour a cousin, aged 34, a miller's son, born at Jevington.
Joseph and Mary's children were: