Stillwater police Capt. Kyle Gibbs told The Associated Press that three people were killed and 22 were injured in the crash Saturday morning.
The driver has been arrested on a charge of driving under the influence. Gibbs said the woman's sedan crashed into the motorcycle of an officer who was working security at the route, then into the crowd of people.
Dave Kapple of Houston told the Stillwater News Press that he and his son were about 10 feet away when they saw the vehicle barreling into the crowd.
"We heard somebody scream, 'Look out!' (The driver) plowed through a police motorcycle, and then a crowd of people," Kapple said. "People were flying everywhere."
Konda Walker, from Anchorage, Alaska, was attending the festivities ahead of the homecoming game between Oklahoma State and Kansas.
"At first we thought it was part of the show," Walker told the News Press. "People were flying 30 feet into the air like rag dolls."
School president V. Burns Hargis said the football game will be played as scheduled Saturday afternoon and the victims will be memorialized at the game. A team official told ESPN's Jeannine Edwards that the school's marching band likely will not accompany the team on their walk to the stadium.