Henderson fired a final-round two-under par 70 at Oahu’s Ko Olina Golf Club course to finish 72 holes in Hawaii on 16-under par 272 for a four-stroke victory over South Korea’s Ji Eun-hee.
Post, 70, claimed eight tour titles from 1968 through 1981.
“It’s amazing to be mentioned in the same sentence with Sandra Post,” Henderson said.
Henderson, 21, also equaled the best showing by any Canadian man on the US PGA Tour, with Mike Weir and George Knudson having each won eight career titles.
“It has just been surreal the last few years,” Henderson said. “It’s just really amazing to get this win to tie Sandra and Mike Weir too.
“I’m so happy. I’m just glad I could come out on top.”
Henderson, who shared the third-round lead with American Nelly Korda, won her first LPGA title at the 2015 Portland Classic as a qualifier. She won twice each in 2016, 2017 and 2018 with her lone major title coming at the 2016 Women’s PGA Championship.
Henderson, who shared the lead with American Nelly Korda when the day began, opened with a bogey but bounced back with birdies at the third and par-5 fifth holes to remain atop the leaderboard.
She birdied the par-4 11th after driving to the fringe of the green to stretch her lead to three strokes over 10th-ranked Korda and 20th-ranked Ji Eun-hee.
Birdies at the par-5 13th and 14th holes pulled Thailand’s Ariya Jutanugarn to 14-under, two back of Henderson, but the world number three missed a 20-foot par putt to bogey 15 and fall three adrift.
Henderson held fast, sinking a clutch eight-foot par putt at the par-3 16th to maintain her margin.
Rivals were unable to close the gap and deny her a historic triumph alongside her sister and caddie Brittany with her parents watching from the family home in Smiths Falls, Ontario.
“My parents have sacrificed so much for us to have this dream out here, to make our dream a reality,” said Henderson.
Thailand’s Ariya Jutanugarn and Australian Minjee Lee shared third on 277, one stroke ahead of American Danielle Kang, Mexico’s Gaby Lopez and South Korea’s Choi Hye-jin.
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