Cort rejoins Peter Taylor at Crystal Palace to replace Fitz Hall, who recently joined Wigan after they met the £3million release clause in his contract. It's the first signing Taylor's made since taking over at Selhurst Park. Cort pens a three-year deal.
The 26-year-old has been with City for the last two seasons after joining on a Bosman free transfer from Southend, and played 91 times, scoring 10 goals.
New manager Phil Parkinson is to seek a replacement for Cort to provide competition for Damien Delaney and Sam Collins. City also have Danny Coles returning from injury in the opening months of the new season.