Where were the forefathers of Francis Scott Key From?

Answer 1

Many were from Scotland (or more properly Scotland via Ireland)

Key's father, John Ross Key, was of "Scotch-Irish" descent (from John Ross, an agent of Lord Baltimore)

Genealogists say the Key family was descended from the Scottish MacKays
http://www.chicago-scots.org/clubs/History/Names-K.htm

Answer 2

Francis Scott Key (August 1, 1779 – January 11, 1843) was an American lawyer and amateur poet who wrote the words to the United States national anthem, "The Star-Spangled Banner".

He was born to Ann Louis Penn Dagworthy (Charlton) and Capt John Ross Key at the family plantation Terra Rubra near Frederick, Maryland.