Donald, Donaldson
Donald, Donaldson—These two names, and there are about a dozen more forms, are the later anglicised forms of McDonald. (In Irish Gaelic Mac Dómhnaill, in Scottish Gaelic Mac Dómhnuill).
Alphabetical Index of Anglicised Surnames in Ireland
See also Woulfe’s Irish Names and Surnames
… and O'Hart's Irish Pedigrees