Park, the 2002 champion and the only player left in the field with a USGA title, rolled to a 6 and 4 rout of Joanne Lee in her semifinal match.
'This is totally where I expected to be,' Park said. 'I'm happy with where I stand.'
Kim defeated Juliana Murcia Ortiz, 2 and 1 -- a victory that came one day after Murcia Ortiz knocked off U.S. Women's Open co-runner-up Morgan Pressel in the third round.
Making her first appearance in the Girls' Junior, Kim needed 20 holes to beat Ya-Ni Tseng in round three Thursday before ousting Stephanie Connelly in the quarters.
'I'm really happy,' Kim said in broken English, before joking, 'I'm tired. Today is only 18 (holes), right?'
Park and Kim, both 17-years-old and each born in Korea, will meet in the 18- hole championship final beginning at 11:00 a.m. (ET) on Saturday.
After moving 2-up through the first three holes, Park made the turn leading by three and went 5-up after rolling in a birdie putt at the par-5 12th.
'In order to beat her, you have to birdie the hole she doesn't,' said Lee.
Kim took the lead for good at No. 11, and 2-up with two to play, she closed out the match on the 17th when Murcia Ortiz couldn't make a 12-foot putt.
'I didn't play the best,' said Murcia Ortiz. 'I left them where I shouldn't. She's really consistent. She plays really good. I hope she can win the tournament.'
The U.S. Girls' Junior was established in 1949 and is open to any female golfer who has not reached her 18th birthday by the close of the competition and has a USGA Handicap Index that does not exceed 18.4. The Girls' Junior is one of 13 national championships conducted annually by the USGA, 10 of which are strictly for amateurs.