[1] Born in Frenchwood House, Lancashire,[2] to a recusant English Roman Catholic family able to trace an uninterrupted pedigree back to Conishead Priory in 1325, Gillow was the son of a magistrate, Joseph Gillow (1801-1872), and his wife, Jane Haydock (1805-1872), a descendant of Christopher Haydock, a Lancashire politician and a member of another prominent recusant English Roman Catholic family, the Haydocks of Cottam.
[2][3] Joseph Gillow was educated at Sedgley Park School, Wolverhampton (1862-1863) and St Cuthbert's College, Ushaw (1864-1866), where his brothers and uncles had studied for the priesthood.
[4] At Ushaw, Gillow developed an abiding interest in Lancashire Catholicism, resulting in the publication of The Tyldesley Diary in 1873.
[5] In marrying into the McKennas, Gillow secured himself a private income which allowed him to pursue his antiquarian interests.
[6] Gillow published various researches into the history of Roman Catholicism in Lancashire, but his greatest achievement was A Literary and Biographical History, or Bibliographical Dictionary of the English Catholics: from the Breach with Rome, in 1534, to the Present Time (5 vols, 1885-1902), available in Google Books.