Kris Commons' first home goal since his move from Nottingham Forest put Derby on the way to a comfortable victory.
Scotland international Commons beat Owls goalkeeper Lee Grant with a low shot from 12 yards after failing to make the most of an early header.
Marcus Tudgay headed straight at Derby goalkeeper Roy Carroll from six yards out before Miles Addison converted Commons' cross to make it 2-0.
A stunning left-footed drive from Jordan Stewart completed the scoring.
Derby manager Paul Jewell: "Brian [Laws] said he'd seen our last two home games and said they had a good chance to beat us. That fired us up a bit, and I thought we were by far the better side.
"It was a comprehensive 3-0 win, and it could have been five or six.
"But we are not getting too carried away, because we still need to improve the squad, but we've got a decent spirit, we are getting better, and we are moving in the right direction."
Sheffield Wednesday boss Brian Laws:
"I've been in there [the dressing room] for an hour with the players because we seem to be psychologically a different team away from home.
"We are very resilient at home, and have only conceded a few goals, but away we have let in a bucketful.
"We had a great chance to get in the top eight today, and we are coming away from Derby very disappointed in the manner in which we have lost."
Derby: Carroll, Connolly, Davis, Nyatanga, Stewart, Barazite, Green (Zadkovich 88), Addison, Commons (Kazmierczak 87), Villa (Ellington 79), Hulse. Subs Not Used: Bywater, McEveley.
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