Rams substitute Giles Barnes' superb last-minute volley rescued a point for Derby in an entertaining game at Ninian Park.
Centre-back Glenn Loovens opened the scoring for Cardiff with a powerful header on 52 minutes and Michael Chopra added a brilliant second 22 minutes later.
Derby forward Steve Howard brought Derby back into the game after Cardiff's first with a top-corner header on 66 minutes.
Both sides wasted good opportunities in an even first half, but the best of the chances fell the way of the home side.
Chopra, returning from a one-match suspension, had the best of Cardiff's chances but spurned a number of good positions.
His first opportunity came on 23 minutes when he received the ball on the right from Joe Ledley, but his shot was wide of the target.
Chopra had an even better chance after 40 minutes when he was put through on goal by a deft touch from strike partner Steve Thompson, but dragged his shot to the left of the goal.
Derby competed well in midfield but rarely threatened the Cardiff goal. On-loan striker Jonathan Stead thought he had put the visitors ahead on 32 minutes but his left-foot strike was disallowed for a shirt pull.
Both sides raised the tempo in the second half and it was Cardiff who struck first, seven minutes after the restart.
Loovens scored his first goal of the season when he rose unmarked to head home from a Paul Parry corner.
Derby clawed their way back into the game 14 minutes later when Howard out-jumped Cardiff captain Darren Purse at the back post to nod home a Richard Jackson cross.
The hosts regained the lead eight minutes later when Parry found Thompson with a low cross and he expertly laid the ball off to Chopra, who drilled a shot low into the bottom corner.
Just when City thought they had done enough to take all three points Barnes rifled home a 20-yard volley from the edge of the area to salvage a point for Derby.
The equaliser left County in 12th position in the table, five points off the play-off places.