- The Kirwans of Galway city were established at Cregg Castle in the parish of Annaghdown, barony of Clare, county Galway, by the mid 17th century. Under the Acts of Settlement they were regranted 3,634 acres. Their estate included lands in the parishes of Annaghdown, Lackagh and Kilcoona, barony of Clare, Dunmore and Addergoole, barony of Dunmore, county Galway and in the barony of Clanmorris, county Mayo. In November 1856 they advertised an estate of 5,885 acres for sale in the Encumbered Estates' Court and are recorded as still owning 4,308 acres in the 1870s. In 1803 Patrick Kirwan leased Cregg Castle and demesne to Francis Blake and went to live at nearby Baunmore, where his descendants were still resident in the early 20th century. Francis Blake is reputed to have won Cregg Castle in a game of cards. Richard Kirwan, the scientist was an 18th century member of this family. In 1856 Richard Andrew Hyacinth Kirwan advertised for sale 5,885 acres in the baronies of Dunmore and Clare. These lots were eventually sold in May 1857 to Nicholas Kirwan and Mr. Courtney. Parts of the estate of Denis Agar Richard Kirwan were vested in the Congested Districts' Board in July 1906 and April 1907 and negotiations were in progress for a further 1,000+ acre in March 1916.
- The Kirwans of Woodfield, parish of Boyounagh, barony of Ballymoe, county Galway, were a junior branch of the Kirwans of Cregg. They were particularly well known for fighting duels. Three generations of Kirwans lived at Woodfield during the 18th and early 19th centuries. They lost their estate when the Tuam Bank collapsed in 1815. By the time of Griffith's Valuation Woodfield belonged to the Handcocks.