And the versatile defender, who played his part in the Pilgrims reaching the National League North promotion final, has agreed to stay on for another campaign.
Ferguson, 21, made 36 appearances and scored vital goals in wins against Kettering Town and Brackley Town.
"It's great news that Keenan is onboard for the new season," Cox told bufc.co.uk.
"He showed his versatility by moving across to the left when required and he ensures we currently have three really talented full-backs on the books.
"Keenan really developed during the course of the season and popped up with two crucial goals in the final few matches."