Liam Cooper has left Hull City after signing a two-and-a-half-year deal with Chesterfield.
The clubs have agreed an undisclosed fee for the 21-year-old defender.Cooper had been on loan at the League Two club since November.
He has become a fans' favourite at the Proact Stadium after a string of impressive performances.
Homegrown Cooper made his debut for the Tigers as a 16-year-old in a League Cup tie against Swansea in 2008.
Phil Brown handed the former Malet Lambert boy a surprise Premier League debut against Liverpool at Anfield, where he faced an on-fire Fernando Torres. The Tigers went down 6-1.
Loan spells at Carlisle and Huddersfield helped him mature and after stringing together a seven-game sequence in the first team at the end of last season he might have hoped to push on as he entered the final year of his contract.
However, after Steve Bruce extended his options in central defence by bringing in Abdoulaye Faye and Alex Bruce, Cooper found himself surplus to requirements.
He made a total of 17 appearances for City.
