Henderson broke a tie with Sandra Post for the Canadian career victory record on the LPGA Tour and also moved ahead of George Knudson and Mike Weir (PGA Tour) for the overall country mark.
"That's really cool," Henderson said. "Earlier this year, to get my eighth win and to tie that record was a huge deal for me. To now break through, that is awesome. I'm just really excited for the rest of the summer and hopefully many more wins in the future."
With caddie/sister Brittany and mother Darlene looking on, father Dave sprayed her with champagne to celebrate.
"It's really special," Henderson said. "I'm so happy that both my mom and my dad can be out here to watch my sister and I win this. It's always special when they're here, especially on Father's Day."
The Lotte Championship winner in April in Hawaii, Henderson matched the tournament record of 21 under she set in 2017 (when the course played to a par of 71), a mark tied last year by So Yeon Ryu. Henderson opened with consecutive 64s, playing 30 holes Friday after rain delayed the start Thursday, and had a 69 on Saturday to take a two-stroke lead into the final round.
"It's a lot like the courses I grew up playing back home in Canada," Henderson said. "I love it out here. Just trying to hit good shots and hopefully make a lot of birdies. Didn't make as many as I wanted, but just enough."
Her lead reduced to a stroke after a bogey on the par-4 16th, she three-putted the par-5 18th from 45 feet for the winning par.
"When I was walking up here, I thought maybe I would have to birdie or eagle this hole to get the job done, but when I looked at the scoreboard, I was sort of shocked that all I needed to do was three-putt and par," Henderson said. "I'm really grateful about that, because I was shaking pretty bad on those last couple putts."
Thompson followed her course-record 62 in the third round with a 68, closing with an eagle for the second straight day. The 2015 winner at Blythefield, Thompson was coming off a victory last week in New Jersey.
"Unfortunately, I didn't hit it that great today, but I made some really good putts on my second nine," Thompson said. "I had a little bit of a muscle spasm in my shoulder all day, but it is what it is. You can't control that. So, overall, great week."
Hataoka shot 65, also making an eagle on the par-5 18th. Oh had a 66, and Altomare shot 68.
Jennifer Kupcho, four strokes behind Henderson entering the day, had a 76 to drop into a tie for 23rd at 11 under in her third professional start. The former Wake Forest star won the inaugural Augusta National Women's Amateur in April.
The KPMG Women's PGA Championship, the third major championship of the year, is next week at Hazeltine in Minnesota.