In the Scottish Gaelic and Irish languages they are patronymic, referring to an ancestor with given name Donald.
[2] According to Alex Woolf, the Gaelic personal name is probably a borrowing from the British Celtic Dyfnwal.
In Ireland the name is largely from this root but may sometimes be a synonym for MacDonnell, which itself may be of distinct Scottish Clan Donald galloglass or native Irish origins.
[12] In contemporaneous data from the United States, coast-to-coast distribution of both "Macdonald" and "McDonald" appears in 1880.
[13][14] Looking back to 1840 in the United States, the prevalence of "McDonald" is far greater than that of "Macdonald", with concentration in the Ohio-Pennsylvania-New York corridor.