McCoy has penned a 12-month deal.
McCoy, with 31 appearances, was among the leading regulars for Blues Under-23s this season.
And he was instrumental in helping to the Development Squad to the PDL North runners-up spot and the Final of the National Play-Offs.
The 21-year-old was signed by Blues from non-league after a successful trial period.
That was at the back end of the 2016/17 season, when McCoy was making waves in the Southern League with Beaconsfield.
And the former FAB Academy star was preparing for life outside of football in the building trade after a succession of other try-outs came to nought.
But he has emerged as one of the most consistent, and dangerous, attacking midfielders for the Under-23s, developing in all areas of his game since joining the Blues ranks.
McCoy was due to be out of contract at the end of next month.
But Blues offered him new terms and he joins Remeao Hutton, Jake Weaver and scholars George Baker, Ben Forrest, Zach Jeacock and Jack Concannon from the Under-23s in committing to the Club.