By the mid 18th century the O'Learys were established at Coomlogane, in the parish of Drishane, in the Millstreet area of county Cork. Helen, the only child of the O'Leary of Millstreet, married, as his second wife, Denis McCarthy of Glynn, county Cork, a descendant of the McCarthys of Drishane and Dooneen. Denis and Helen McCarthy had no children but she left her estate to her stepson, Denis McCarthy, on condition that he take the name O'Leary. In 1812 Denis McCarthy O'Leary married Leonora Howley of Richill, county Limerick and their descendants continued to reside at Coologane until the early 20th century. In the 1870s the McCarthy O'Leary estate amounted to 5,896 acres. In 1788 Denis McCarthy leased almost 1,000 acres from Dowman, Harman and Phillips in the barony of Duhallow. Part of the fee simple of these lands was advertised for sale in January 1862. J. McCarthy O'Leary was the lease holder.