Joe Garner gave Town a lifeline midway through the second-half but two goals from Sam Winnall maintained Derby’s promotion push.
The Rams haven’t lost since Callum Connolly’s goal beat them at Pride Park in November and Winnall gave them the perfect start at Portman Road with a header early on.
The striker extended his side’s lead soon after the break with a superb strike but Garner got Blues back in the game with a close range header.
Town pushed for an equaliser but couldn’t find a way past Scott Carson as Derby made it six games unbeaten.
Town made four changes from the side that drew with QPR on Boxing Day, Kevin Bru, Grant Ward, Bersant Celina and Jordan Spence back in the line-up.
Former Town loanee Tom Lawrence was prominent for the visitors in the opening exchanges, twice crossing into the box with Luke Chambers clearing on both occasions.
It was from Lawrence’s corner on 12 minutes that the Rams went ahead, Winnall allowed too much room to head into the corner of the net.
Derby should have been two up a minute later, a mix up between Chambers and Adam Webster allowed Matej Vydra a clear run but with a goal beckoning, he blasted high over the bar.
Martyn Waghorn released Jonas Knudsen with a terrific pass, the Denmark international’s cross cleared by Richard Keogh, then Connolly tested Carson with a header as Town responded.
Ward tracked Lawrence inside the Town box to cut out the danger as Derby continued to carry the main threat though, George Thorne firing over from 25 yards then Chambers threw himself in the way of Lawrence when another goal looked on the cards.
Connolly was inches away from an equaliser at the other end from Waghorn’s corner while Vydra was unable to direct his shot at full stretch from Thorne’s excellent pass.
Johnny Russell, not for the first time, escaped down the Derby right and made in-roads into
Town’s danger area and it needed Spence to clear off the line.
Celina rallied for Blues and had Carson diving across goal to see a right foot drive go just wide, then Connolly had a shot deflected as Town looked to get back on level terms before the break.
Ward tested Carson from distance as the second-half got underway but Town were stung on 48 minutes when Winnall smashed a sensational strike into the roof of the net from 25 yards.
Bart Bialkowski did well to smother the threat from Vydra at his nearpost, Keogh clearing from Knudsen as Blues looked to get a foothold in the game. Garner’s shot blocked by Curtis Davies.
Winnall fired over after terrific play by Vydra set him up, Lawrence was just over with a trademark piledriver, then Bru was just wide with a diving header from Ward’s cross.
Town got back in the game on 65 minutes, Waghorn’s corner met by Garner’s forehead from close range, the striker’s seventh goal of the season.
Lawrence made way for Andreas Weimann in the game’s first change, the Wales international receiving warm applause as he left the field. David McGoldrick joining the action for Bru.
Town’s injury woes continued with Webster forced off, Dominic Iorfa the replacement. Keogh showed his quality with a run from deep that set up Winnall but he couldn’t find the net.
Ward’s volley was blocked inside the box as Town pressed for an equaliser, Knudsen heading into the sidenetting in added on time.
Town: Bialkowski, Spence, Chambers, Webster (Iorfa 74), Knudsen, Ward, Bru (McGoldrick 70), Connolly, Celina, Garner, Waghorn. Subs not used: Crowe, Smith, Sears, Kenlock, McDonnell. Booked: Webster.
Derby: Carson, Forsyth, Keogh, Russell, Lawrence (Weimann 70) Wisdom, Winnall (Baird 88), Vydra (Olsson 81), Davies, Thorne, Huddlestone. Subs not used: Mitchell, Martin, Pearce, Nugent.
Att: 17,267