The 20-year-old finished at 21-under 267, capping the emotional victory in front of a large, adoring gallery with a short birdie putt on the par-4 18th at a chilly and rainy Wascana Country Club.

"Truly amazing, dream come true," Henderson said.

"The crowds were incredible all week. Today was incredible.

"To have their support and then to play as well as I did and to hoist this trophy, I'm just so excited.

"... to have my family and my close friends and the LPGA Tour stars come out and shower me with champagne, I mean, I still have some in my ear, so it's not that fun, but it was just so amazing."

Henderson rolls in a short birdie putt at the 18th to win her national Open by four shorts. PHOTO: Vaughn Ridley/Getty Images.

Jocelyne Bourassa is the only other Canadian to win the national championship, accomplishing the feat in 1973.

Henderson earned $337,500 ($A460,000) for her second victory of the season and seventh of her LPGA Tour career.

Angel Yin was second at 17 under after a 68 while Jennifer Song (67) was six back of Henderson in solo third.

Australian duo Minjee Lee (68) and Su Oh (69) finished in four-way share of fourth at 14 under.

Lee had six birdies and two bogeys on Sunday while Oh's roller-coaster final round included an eagle, five birdies and four bogeys.

Katherine Kirk closed with a 70 for a seven-under total while Hannah Green's 74 left her at three over for the week.

Three-time Canadian Open champion Lydia Ko (69) and top-ranked defending champion Sung Hyun Park (71) were among the group at 13 under and tied for eighth.