Louisa Catherine Johnson Adams
Only First Lady born outside the United States, Louisa Catherine Adams did not come to this country until four years after she had married John Quincy Adams. Political enemies sometimes called her English. She was born in London to an English mother, Catherine Nuth Johnson, but her father was American--Joshua Johnson, of Maryland--and he served as United States consul after 1790.
http://www.whitehouse.gov/history/firstladies/la6.html