Dargan is a surname. Notable people with the surname include:
It is believed that Cromwell, during his conquer of Ireland, decreed that the Gaelic names used by the inhabitants were to be outlawed and replaced with more 'English' sounding surnames. Whether each individual Gaelic surname was replaced with an equivalent sounding English version or whether all inhabitants of a village were told to adopt the English surname is unknown.
References
Dargan (surname) Wikipedia(Text) CC BY-SA