Chun, whose two previous wins on the U.S. tour had both been majors, finished with a 16-under 272 total, three strokes ahead of England's Charley Hull (71) at the SKY72 Golf & Resort in Incheon, west of Seoul.
Korea's Park Sung-hyun (69), Australian Minjee Lee (70), Thai Ariya Jutanugarn (71) and American Danielle Kang (72) were a stroke further back tied for third.
With nine wins on the Korean women's tour before making the switch to the United States for the 2016 season, Chun's popularity remains undimmed at home and Sunday's galleries were again swelled by her huge army of followers.
Organisers said almost 32,000 fans came out for the final round alone, with the total for the four days at over 68,000.
Chun carded seven birdies against a solitary bogey to move past overnight leader Hull and claim her first win since the 2016 Evian Championship.
And the victory seemed to take a weight off her shoulders.
"I'm so happy to win in front of these fans," a tearful Chun told Korean television, adding that she hoped it would mark a "turning point" after two winless seasons.
World number one Park was disappointed not to have laid down a challenge on the final day.
"As I mentioned earlier, this was a course I was confident with and in the past had scored very well here, and I really wanted to win. But today I wasn't able to bring my 'A game,'" she said.
"The world ranking, it always changes so that wasn't really a big factor. But once you win an event, that lasts forever, so I think winning was more important for me."
The U.S. tour continues its end-of-season Asian swing next week in China with the inaugural Buick LPGA Shanghai.
(Reporting by Peter Rutherford; Editing by Amlan Chakraborty)
