Muldoon (Irish: Ó Maoldúin) is an Irish family name. It is represented throughout the world where descendants of emigrants of people bearing that name have settled; e.g. U.S., Canada, Australia, New Zealand, South Africa and other countries.
Muldoon is an anglicisation of the Irish surname Ó Maoldúin, meaning "descendant of Maoldúin". The personal name Maolduin is composed of the elements "maol," meaning "chieftain," and "dún," meaning "fortress," or "chief of the fortress." Máel Dúin was one of the Kings from Mag Rath in Dál Riata, a Gaelic 'kingdom' that covered parts of north-eastern Ulster and south-western Scotland (see List of the kings of Dál Riata), Máel Dúin mac Conaill (died c. 689).
According to The Surnames of Ireland by Edward MacLysaght, there are three distinct septs of Muldoon: Galway (around Uí Maine), Clare (whose names were generally Anglicised to Malone), and in Co. Fermanagh where the name is most common.
The family motto is Pro Fide Et Patria, Latin for "For Faith and Country".