With the player agreeing to a three-year deal it is now up to Stockport County and Crewe to decided on the compensation package for the Welsh U-21 keeper.
If both teams fail to agree on a fee then it would more than likely go to a tribunal.
The on off saga of whether Williams would sign had been going on for a few months with the player also being linked with Blackburn Rovers, Bolton Wanderers, Derby County and Swansea City in previous months.
During his five years at Crewe Williams failed to make any first team appearance and felt that he could not trust the club and this after being given assurances about being the clubs number one keeper for the following season.
During the close season Crewe had delved into the transfer market and snapped up Birmingham City keeper Adam Legzdins and Southend United's Steve Collis both on a free. With them signing, it was only a matter of time when Fon Williams would leave the Alex.
Fon Williams told County TV "I've spoken to Wayne (Hennessay) a lot about County, and he told me that if an opportunity arose to join them I shouldn't hesitate."