DESMOND is the name of a place in Ireland. The ancient boundaries of Desmond included most of today's County Cork and County Kerry, in the province of Munster.
"Desmond" is the Anglicized spelling of the Gaelic "Deasmhumhnaigh", which roughly translates to "south Munster".

The origin of DESMOND when used as a surname is less clear. There are three competing theories:

1) Families using the DESMOND surname are descended from the Gaelic sept "Ui Deasmhumhnaigh" which means "man of south Munster".

2) Families using the DESMOND surname are descended from the "Earls of Desmond", a branch of the Anglo-Norman FitzGerald family, who settled in Ireland in the late 1100's, and a noble line which officially died out in the early 1600's.

3) Families using the DESMOND surname are descended from another Gaelic sept or septs (such as MacCarthy, "Kings of Desmond"), and are part of a sub-clan which took the surname at some point during the middle ages.

Each theory has its strengths and weaknesses, and its possible that any number of the three theories account for the ancestry of modern-day Desmonds.