I found something: Thomas HART/HARTE m Mary GERAGHTY; residence given Derryfadda, Mayo. He d 1879 Castlebar, age 79. found here:
https://www.british-genealogy.com/archive/index.php/t-65111.html w info if you want death certificate. This may be clue where to look.
Also, John O'HART (famous genealogist) was native of Crossmolina, b 1824.
Acc. to a Henry Travers HART of London 1907, HARTs were from Donegal. There were a group brought in fr. Donegal as weavers for the flax, my ancestor FOY turned into a farmer of flax.
Martin HART of Glenhest (Addergoole?) d 1900 age 42; m Catherine CROFTON abt 1894 (children 1895-1901) Maria, John, Julia, Martin.
One more: Edward HART of Tawnag East, Kilmainemore, Ballinrobe, Co Mayo. He m Cath. Linsky of Ireland. Son William b 4 Aug 1819 Ballinrobe, who came to Ohio, USA and m Margaret CULL.