The 6-11 center, who averaged almost a double-double for the Big 12 champions, is projected by most experts as a high first-round pick.
"The last three years have been pretty special," he said.
Blessed with a wingspan greater than most men his height, Aldrich averaged 11.3 points and 9.8 rebounds for the Jayhawks, who were the overall No. 1 seed in the NCAA tournament before they were upset by Northern Iowa. He also set a team record with 125 blocks.
The Jayhawks are still waiting for a decision by freshman swing man Xavier Henry, their second-leading scorer.
It would have been a surprise if Aldrich had elected to remain in school. His father, Walter Aldrich, is a construction worker who's been put out of a job by the recession.
"We've known this was going to happen since last year," said coach Bill Self. "To be real candid with everybody, and I think Cole would agree with this, I would strongly discourage him from coming back.
"I think he paid his dues here and I do think it is time for him to move forward into another chapter. He has made a lot of sacrifices -- his family has -- to come back in a time when he didn't have to. We're all very proud of him."
Aldrich, a native of the Minneapolis area, said he planned to hire an agent soon.
"First of all, I want to thank everybody just for the opportunity I've had here," said Aldrich. "It's been a fun one."
Aldrich referred to his paternal grandmother, who died during this past season after a long illness.
"I don't want to get choked up or anything, but the last three years have been pretty special. It's been a lot of highs, a few lows with my grandma ..."
He paused and looked down.
"It's been a special time for me and my family. I've talked with them extensively. We went through somewhat of the same process last year in figuring out what I wanted to do. I think my time has come in my life to change the chapter and go from one great chapter to hopefully start another great chapter in life."
Aldrich and senior guard Sherron Collins, who are close friends, made a joint decision last spring to return this season and pursue an NCAA championship. But that was thwarted when Northern Iowa upset them in just the second round.
He was a reserve on the 2008 national championship team.
"We were all upset that it had to end so short," he said. "Being a part of a team that went and played all six games and then playing three games last year, we had high goals. But those goals are going to be there again. And I hope the team next year is going to be there again. I'm really going to support those guys."
Aldrich, an academic All-American, was named to The Associated Press third-team All-America squad on Monday.
"He's represented himself and this school in a way that has been nothing but first class," said Self. "He's going to go ahead and finish up school and get his degree. He promised us that."
Self said Aldrich's projected draft position was "almost irrelevant right now with Cole."
"I think we all know that he's going to go pretty high," Self said. "Whether he goes five or 14, I don't really know. I think so much of it, and Cole will agree with this, will be dependent on what other bigs are in the draft and when certain teams draft in need of a big."