John O'Hart has been adopted as the patron of the Crossmolina Heritage Society for its Summer School.

He was born in Crossmolina and went to school there. He joined the R.I.C. but after two years, resigned and became a teacher. He married Elizabeth Burnet in 1845. In 1856, he took up a position in Ringsend N.S.

Later, he devoted his time to antiquarian and genealogical research. The first volume of his work was published in 1875, the second in 1878 and the third in 1881.

His most important volumes were 'Irish Landed Gentry', 'When Cromwell Came to Ireland' in 1873 and 'Irish Pedigrees', in 1880.

He also wrote 'The Last Princes of Tara' ‚ and contributed to 'Hibernia', a monthly magazine published in London.