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That condemned Paul Jewell's team to a sixth Championship defeat in nine games and leaves them five points above the relegation zone.
Although Derby had plenty of possession, they did little with it and there were too many long balls to seriously trouble an Ipswich defence in which Ivan Campo and Gareth McAuley were outstanding.
To add to Derby's woes, striker Nathan Ellington went off after nine minutes with a hamstring injury and Jordan Stewart was given a straight red card for a reckless high challenge on David Norris 12 minutes from the end.
There were boos and some calls for Jewell to go at the end of a performance which was another huge disappointment.
Ipswich always looked capable of taking the points after Walters had become the latest striker to profit from Derby's careless defending.
The home defence was again in disarray when Ben Thatcher curled in a cross from the left and Walters dived full length in front of goalkeeper Stephen Bywater to glance the ball inside the left-hand post.
There were a few anxious moments in the Ipswich defence but Richard Wright had only two real saves to make in the game.
The closest Derby came to equalising was in the 56th minute when Steve Davies, on as a second-half sub for the out-of-touch Rob Hulse, got the better of Campo and struck a post with a low right-foot shot.
After that, Derby huffed and puffed but rarely threatened to get back in the game.
Their chances receded even further when Stewart was sent off and Derby now go into next weekend's tricky FA Cup tie at Forest Green Rovers with confidence at a low ebb.