The visitors had only themselves to blame, having passed up a number of excellent first-half opportunities, and once Ipswich scored within a minute of the interval, the feeling was County had missed their chance.
That was confirmed when Darren Currie struck midway through the second half, and in the end Ipswich coasted to a comfortable win, ending an eight-game winless run - the last four all defeats - going back to February 25th.
An open game saw Derby threaten early, with Shane Supple spilling a low Michael McIndoe cross, only for Owen Garvan to clear the danger, before Morten Bisgaard shot over from 30 yards.
It was almost 20 minutes before Ipswich threatened, when both Currie and Matt Richards shot wide, either side of a Supple save to keep out a Giles Barnes header from a Tommy Smith cross.
Lee Camp had to parry a shot around the post from Jim Magilton - making his farewell Portman Road appearance - before Inigo Idiakez slid in Bisgaard, but Supple was out quickly to block.
Magilton had a chance soon after when he brought down a sweeping Garvan crossfield ball and cut inside, but fired wide.
Supple made a fine low save to keep out a Bisgaard shot, before Fabian Wilnis produced a great block to deny Barnes a shooting opportunity.
Smith shot wide from an angle when he had team-mates better placed and then teamed up with Bisgaard to create a headed opportunity for Barnes, which Supple saved.
Derby missed a great chance on 41 minutes when Supple's poor kick went straight to Idiakez, who picked out Smith, but the striker placed his shot wide when clean through.
The visitors were made to pay 54 seconds after the break when Nicky Forster took aim from 20 yards after receiving a Garvan pass and found the top right-hand corner, taking him to six goals for the season and making him Ipswich's leading scorer.
Danny Haynes saw a diving header saved by Camp as Ipswich made a lively start to the second half, and then Currie's curling free-kick narrowly evaded a diving Forster.
Forster headed over a Richards cross from six yards before Marc Edworthy had to clear a dangerous low Forster cross as Richards closed in for the finish.
Little had been seen of Derby in the second half but on 62 minutes Bisgaard received the ball just inside the box and sent a curling effort not far wide of goal.
Town doubled their lead on 66 minutes when half-time substitute Jaime Peters, a replacement for the injured Magilton, crossed into the middle, Derby cleared to the edge of the box and Currie's volley beat Camp, who appeared to be deceived by a late swerve on the shot.
Forster was denied with another headed chance by Camp, headed another effort over and then shot well over after being found by a long Supple clearance, as Ipswich searched for more goals.
In the end though, they were happy to see out the remaining minutes with Derby less of a threat as the match went on, to at least send the home fans away for the summer with a spring in their step.