The game will take place on Saturday, February 14, unless it is moved for TV coverage.
Reading overcame Cardiff City 2-1 in South Wales on Saturday thanks to goals from Oliver Norwood and Hal Robson-Kanu.
Many Reading fans were hoping for either a glamour tie at a Premier League side or a winnable home fixture, with the trip to Derby somewhere in between.
But Steve Clarke has a fantastic record in the FA Cup and his side have already won away from home at Championship opposition twice in this cup run, so the Royals will head to Derby in confident fashion.
Reading are back in Championship action tomorrow night when they travel to Millwall.
Visit the Chronicle website for live coverage of the game from the New Den (7.45pm ko).
Comments: Our rules
We want our comments to be a lively and valuable part of our community - a place where readers can debate and engage with the most important local issues. The ability to comment on our stories is a privilege, not a right, however, and that privilege may be withdrawn if it is abused or misused.
Please report any comments that break our rules.
Read the rules here