The centre-back began his career at Pride Park, progressing through the youth system to make his first-team debut in May 2000. He went on to make 100 appearances for the Rams.
He had been without a club since being released from Cardiff City at the end of last season.
The 30-year-old has been training with Derby for the last month in a bid to prove his fitness.
Derby boss Nigel Clough told the club's website: "We have said all along that as long as he proved his fitness to us, we would get him signed up on a year's contract."
The former England Under-21s player has struggled with injuries in recent years and underwent back surgery at the beginning of the year.
"Chris hasn't played for almost two years so we have to be a bit patient with him in terms of getting back to match sharpness and secondary injuries he may pick up," Clough added.
Derby, who lost 3-2 at home to League Two outfit Shrewsbury Town in the Carling Cup last night, next travel to Watford on Saturday.