Henderson finished play late Thursday with a hole-in-one on the 15th hole, her sixth hole of the round that started seven hours late.
"I was able to carry it on early this morning," said Henderson, the 2017 winner at Blythefield. "Then I had lunch and came right back and played another 18. I just felt really confident today with my ball-striking, which is awesome, and I rolled in a few putts, too."
The 21-year-old Henderson successfully defended her Lotte Championship title in April in Hawaii for her eighth LPGA Tour victory, tying Sandra Post's Canadian record. George Knudson and Mike Weir share the Canadian mark on the PGA Tour, also with eight victories.
Henderson birdied five of the final six holes in the second round to break the tournament 36-hole record she set in 2017 by two strokes.
"With these soft conditions you can take it pretty much right at it, which I've been doing," she said. "To shoot scores like that you have to have everything kind of working for you and you have to get some breaks along the way, too, which I did. I think playing well last night, finishing off with a hole-in-one before going to sleep was really exciting for me, and I was just able to back it up this morning, which is cool."
Brittany Altomare was second at 13 under after rounds of 66 and 65. She played 31 holes Friday.
"It was long, but we made the best of it," Altomare said. "I've been struggling this year with my putting, which is normally my strong suit, and today and yesterday, I guess last night into today, it just kind of all clicked."
Jennifer Kupcho shot 67-67 to reach 10 under, playing 29 holes Friday. The former Wake Forest star is making her third professional start. She won the inaugural Augusta National Women's Amateur in April and the NCAA individual title last year.
"I've been hitting the ball really well," Kupcho said. "The last couple tournaments I've been struggling with that, so just to hit the ball well has been nice. I hit a lot of greens both rounds. I would just say pretty much everything is going good."
Annie Park was 9 under with a hole left when play was suspended because of darkness. Twenty-eight players were unable to finish.
Angela Stanford (68-68), Megan Khang (70-66), Moriya Jutanugarn (69-67) and Nasa Hataoka (68-68) were 8 under.
Henderson's ace Thursday was one of five in the first two rounds, one off the LPGA Tour tournament record set in the 1999 Mercury Titleholders Championship. Mariajo Uribe, Giulia Molinaro and Haru Nomura also aced the 15th in the first round, and Lindy Duncan had one on No. 7 in the second round.
Henderson played alongside 2015 winner Lexi Thompson and defending champion So Yeon Ryu the first two days.
"It was a really fun group," Henderson said. "Two amazing players and defending champions, so they know how to play this golf course really well. It was a lot of fun making birdies together and just kind of see how they're doing it."
Ryu was 7 under after rounds of 69 and 68. Thompson, coming off a victory last week in New Jersey, shot 70-68 to reach 6 under.
Nelly Korda (68-69) was in the group with Ryu at 7 under.
U.S. Women's Open champion Jeongeun Lee6 was 4 under, shooting 70-70.
The KPMG Women's PGA Championship, the third major championship of the year, is next week at Hazeltine in Minnesota.