At the time of Griffith's Valuation W.R.B. McGuire held the townland of Monacow, parish of Tuam, barony of Dunmore, county Galway. In the 1870s his representatives owned almost a thousand acres in the county.
National Archives of Ireland:
Landed Estates' Court Rentals (O'Brien), McCormick, 10 Feb 1865, Vol 75, MRGS 39/037, (microfilm copy in NUIG)