Chris Martin headed the hosts into the lead from Cyrus Christie's cross after Tom Ince had earlier seen a deflected effort hit the Town post.
The Terriers had chances to get back in the game but Jamie Paterson dragged a shot just off target from 15 yards.
Ince's shot struck the crossbar before sub Johnny Russell wrapped up the victory with a smart curling finish.
It was just a third win in 11 matches for the Rams but victory maintains their hopes of pushing for an automatic promotion place.
Darren Wassall's men are seven points behind second-placed Middlesbrough having played a game more.
Huddersfield were competitive throughout but defeat means they drop to 18th in the table, seven points clear of the relegation zone.
The Rams travel to QPR on Tuesday while Huddersfield host Reading, looking for their first win in four matches.
Derby head coach Darren Wassall: "We believe in Chris Martin but what we did do at Brentford [on 20 February] was have a long chat before the game and say we wanted him firing on all cylinders because he's a great asset to the club.
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"He hadn't scored in open play since October so we decided to leave him out for the Brentford game and he agreed with that decision. Since then, I think it was a weight off his shoulders and his attitude was great.
"He came on at Brentford and scored a wonder goal and he's not looked back since. That's all we've done, we told him we really rate him as a player and he's responded which is full credit to him."
Huddersfield head coach David Wagner: "Derby had to produce one of their best performances today to be able to beat us and so we can leave the stadium with our head up.
"I think there were only some small key points that decided this game and those were in Derby's direction which is why we lost.
"It's important that you trust and believe in yourself and sometimes you get what you deserve and sometimes not. Today I think we didn't get what we probably deserved, which was a draw or maybe more.

In those two decades, the country has come a long way but still faces many problems.
Tour guide
Businesswoman
Cafe owner
Choir mistress
Farmer
South Africa Direct
While many blacks have moved up the economic ladder, poverty remains high, tensions still exist between blacks and whites in some areas and South Africa has one of the highest number of HIV/Aids patients in the world.
For Working Lives, the BBC's Lerato Mbele travelled to Johannesburg to meet five very different South Africans living and working in and around the city.
Hair salon entrepreneur Mankwane Chakela is a proud member of South Africa's growing black middle class. She grew up in a township but now lives in one of Johannesburg's more affluent suburbs.
Hoping to make a similar transition is Jeff Mulaudzi, who runs tours of Alexandra, one of Johannesburg's sprawling townships.
He spotted a gap in the market for adventurous tourists wanting to see the real South Africa and now shows small groups around his neighbourhood.
Another part of the city undergoing a revival is Johannesburg's Central Business District where Nick Christowitz caters to a multi-racial clientele in his impeccably designed and achingly cool cafe.
School choir mistress, Makgopa Gomba, had to flee her township home in the last years of the apartheid era on account of her husband's job as a policeman.
But now, she is back and working in the local community.
White farmer Louis Meintjes says he can trace his South African heritage back to the 1730s.
Farming has never been an easy life but in the past it was more certain.
Derby County remain in fifth place in the Championship after a win over Huddersfield.
[NEXT_CONCEPT]
It is 20 years since South Africa held its first non-racial elections which ended white rule and saw the transfer of power to the African National Congress.