Woodland, 35, produced a final hole birdie to win by three shots on Sunday (Monday NZ time) after holding a one-shot overnight lead over Justin Rose.
It was Woodland's fourth PGA Tour win in his 12-year-career, but his first in a major championship.
He rallied with a birdie at the 14th and never looked like relinquishing his lead.
Koepka, who was tied for third overnight - four shots behind Woodland - carded 68 in the final round, but fell short of his bid to win a third consecutive US Open title after triumphing in 2017 and 2018.
But he could only watch as Woodland held his never and then produced the final flourish birdie for a fourth round 69.