Elgin is a family name noted by a personal correspondent [YEC], used in this case for female members.  In the US it is believed to be mainly a male name, pronounced with a soft 'g' unlike the city.  The origin of the family's usage is not clear but it is probably in respect of the City of Elgin in Morayshire.  ONC only gives Elgin as a place-name and states that the origin is unknown. Our correspondent, however, has noted that the Elgin City website suggests that the derivation may be from Irish Gaelic, possibly introduced by early immigrants:

"It is possible that the name Elgin is a combination of Elg or Eilg, the poetic name for Ireland, and in, meaning little ...  = 'Little Ireland'."