The 21-year-old, who arrived at the club from Nottingham Forest last summer, will now remain with the Rams until at least the summer of 2016.
Derby manager Nigel Clough told the club's official website: "Kieron is a player we have an awful lot of faith in and we think he's going to be a very good player in the future.
"He's got all the right attributes to be an extremely good defender and he's got a good opportunity at the moment, with John out injured, to build up his Championship experience.
"We've been pleased with his progress over the last few months and he's not looked out of place when we've put him in the first team.
"It's pleasing to once again secure the services of one of our promising young players on a long-term contract and that Kieron sees the direction we're moving in."
Derby currently sit 10th in the Championship table.