It is the first All-American WTA final on home soil in eight years, according to the Associated Press.
Vandeweghe, 20, reached the final with a 6-2, 3-6, 6-2 victory against Belgium'sYanina Wickmayer. Vandeweghe enters the final as a "lucky loser," as she failed to make it out of qualifying and only got into the main draw when Bojana Jovanovski withdrew with an injury.
"It's a dream come true for me being in the finals of a WTA event," Vandeweghe told the AP. "Hopefully this is a good omen for the rest of the summer for me."
Vandeweghe had never reached a WTA semifinal until she knocked off Urszula Radwanska of Poland, 6-4, 6-4, on Friday.
Williams beat Vandeweghe in a World Team Tennis match that ended in a nine-point tiebreaker at 5-all last summer in their only meeting.
Williams, the recent Wimbledon singles champion, overpowered Romania's Sorana Cirstea, 6-1, 6-2, in her semifinal.
— From staff reports