https://www.libraryireland.com/names/oh/o-heigceartaigh.php
https://en.wikipedia.org/wiki/Hegarty
In Gaelic the surname is O hEigceartaigh, from eigceartach, meaning “unjust”. The name appears to have arisen first in the area now divided between counties Derry and Donegal, where the O hEigceartaigh were a branch of the Cinel Eoghain, that large group of families claiming descent from Eoghan, one of the sons of Niall of the Nine Hostages, the fifth century monarch who supposedly kidnapped St. Patrick to Ireland. However, today the surname is much more common in County Cork, at the other end of the country. Traditionally, the Cork (O’)Hegartys were claimed as a branch of the more historically prominent northern family, but ecertach was a common personal name in Munster, and it seems more likely that the surname arose separately there. At any rate, O’Hegartys are recorded in west Cork as early as the thirteenth century, and remain strongly associated with the area.
It seems there is not an active clan organisation for your name, at this time.
However, the revival of interest in Irish culture and heritage over the past 100 years has led to the revival of many Irish Clans. In more recent times, increased access to historical archives online, DNA testing and ease of travel to Ireland has led many individuals to explore their own genealogy and connections to Irish Clans. Some of these have gone on to establish Clan Associations in Ireland, the USA, the UK, Canada, Australia, New Zealand and anywhere that the Irish Diaspora has found itself.
Clans of Ireland Ltd invite those interested in Irish Clans to contact them with a view to explore the possibility of reviving your Irish Clan.