Cooks, the Biletnikoff Award winner as the nation's top receiver, set Pac-12 records with 128 catches for 1,730 yards for the Beavers this season.
His receiving yards were tops in the country, and his 16 touchdown catches this season are a school record.
ESPN's Joe Schad had reported Tuesday on Cooks' intentions to enter the draft.
"I look back at it, a lot of the things I did, I couldn't have done without my teammates," Cooks said Thursday. "If it wasn't for those guys, I wouldn't be in the position I am today."
One of the nation's most explosive players, Cooks is projected as a second-round draft choice by ESPN college football and NFL draft analyst Todd McShay, and by an NFL draft advisory committee.
He said he consulted coach Mike Riley and the rest of the Beavers' coaching staff about the decision.
"They didn't try to sway me either way," he said. "They were a great support through this process, just like they've been the entire time I've been here. They're like another family."
The first-team All-American, who is 5-foot-10 and 185 pounds, finishes his Oregon State career with 226 catches for 3,272 yards and 26 total touchdowns (a school-record 24 via catch). He has 3,863 all-purpose yards.
Cooks said he is still interviewing possible agents and isn't quite sure where he'll train. But he is certain he wants to finish school, and already has started online courses to earn his degree in human development and family sciences. He expects to finish next winter.
"I promised my mom I'd get my degree," said the Stockton, Calif., native, who lost his father to a heart attack at age 6.
Because he has not selected an agent, Cooks can still change his mind until Jan. 18, but he said Thursday he was committed to going pro.
Oregon State went 7-6, capping this season with a 38-23 victory over Boise State in the Sheraton Hawaii Bowl.
Robinson, a third-team All-America selection, set Penn State season records in receptions (97) and yards receiving (1,432) for the second consecutive year.
Said Robinson on Twitter:
It was a honor to wear a penn state uniform for 3 years. I will miss my teammates and coaches, blessed for the opportunity and experience!
— Allen Robinson (@Djjango8) January 2, 2014
The Associated Press contributed to this report.