The 35-year-old won the 119th US Open on Sunday, duly denying Koepka a third straight title at Pebble Beach.
Woodland edged out his fellow American by three strokes to clinch his first major title with a 13-under par total. The Kansas-native headed into the fourth round a shot ahead of Justin Rose having passed the Englishman on day two in California.
"Once that went in, it all kind of came out of me, it was special to finish it off here at Pebble Beach," said Woodland, who bagged a birdie on the 18th to clinch the win.
Tiger Woods left 'steaming'
Koepka was humble in losing his crown to Woodland, praising his compatriot for his poise.
"I played great," said Koepka. "Nothing I could do."
"Gary played a great four days. Cool way to go out on 18, to make that bomb."
"He deserves it, he's worked hard and I'm happy for him."