McIlroy’s round included two birdies, a double-bogey and a quadruple-bogey at the par-4 11th hole, where he bent his wedge in frustration after hitting a ball into the water.
"I just hit a bad tee shot into the creek there, and then what you don't want to do as a golfer is follow one mistake with another, and that's what I did," McIlroy told reporters. "And obviously I got a bit frustrated.
“I think that's what this tournament does to you. At one point or another, it's got the better of you, and it definitely did this weekend."
The No. 2-ranked golf player in the world said that the pin locations on Sunday were on the "edge" of being unfair. "I can see the [USGA] trying to protect the scores and stuff," he said. "But the pin position on seven today, for example, was on the back of a slope. "At least put it a couple of yards down so it's on the flat part of the green. They decided to put it on a ridge. It's a U.S. Open."
McIlroy finished in a tie for 41st at 14-over par.
Meanwhile, 32-year-old Englishman Justin Rose bested six-time U.S. Open runner-up Phil Mickelson to win the tournament with a level-par 70 to end one over.
Rose led the group by one going up the difficult 18th and hit a fantastic four-iron approach to set up a par four. Meanwhile, Mickelson tied for second with Jason Day, finishing 3 over par, two strokes behind Rose. Mickelson bogeyed the 13th, 15th and 18th holes on Sunday and double-bogeyed Nos. 3 and 5. He finished with a final-round 74, his worst of the four days in the tournament.