The left-back has secured a two-year agreement with the Premier League outfit, before departing to the Legaue Two outfit for the coming season.
Ferry has been with the Saints since he signed from Bury in 2017.
The 20-year-old, who played 16 times for the club's B team in Premier League 2 last term, will be hoping to make his senior debut for Southampton one day.
Saints academy director Matt Hale said, per the club website: "Firstly, it's great that Will has agreed a new contract with the Club. Will was very consistent with his performances last year and adapted well to a change of position whilst playing in the B team.
"A loan right now is the right move for Will and the next step in his progression with us which will see him develop even further and gain some valuable senior playing experience in the football league."
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