Although born in Liberia, Forko and his family moved to Houston, Texas when he was three. He began his collegiate soccer career at the University of South Carolina in 2002. He played one season there before transferring to the University of Connecticut. At UConn he appeared in 65 matches, notching 3 goals and 15 assists, and was twice named to the Third Team All Big East.
He was selected in the second round, 14th overall, of the 2006 MLS Supplemental Draft by Real Salt Lake.
On 24 March, 2008, it was announced that Forko had signed for the Norwegian Premier League side FK Bodø/Glimt.
Willis' older brother, Sam Forko, played for the MetroStars in 2002.