Cook announced his decision on Wednesday, which means the Hawkeyes are getting their best player back after a trying 2017-18 season.
"I am excited to return to Iowa for my junior season," said Cook. "I am grateful for the opportunities and feedback that I have received from NBA personnel. I am thankful for coach (Fran) McCaffery and the coaching staff for their assistance and patience with me during this process."
Cook averaged team highs of 15.3 points and 6.8 rebounds a game for Iowa, which finished 14-19. But the return of Cook and fellow junior Isaiah Moss -- who also withdrew from NBA draft consideration -- should put the Hawkeyes in position to improve next winter.
Iowa will also bring in prized recruit Joe Wieskamp, perhaps the only recruit more highly touted than Cook in McCaffery's eight seasons with the Hawkeyes.
"We are happy to have Tyler back for his junior season," said McCaffery. "Tyler did well in his workouts and interviews, which will bode well for him next year when he goes through the process again. He has had a significant impact on our basketball team the past two seasons, and we look forward to Tyler improving his overall skill set and being a leader for us next season."