Washington State Patrol Trooper Guy Gill said the pedestrians were in a crosswalk when they were hit about 6:30 p.m. at the intersection with 134th Street.
All three people were taken to Tacoma General Hospital but their current conditions were not known.
Gill said the driver stopped at the scene and told troopers he did not see the people in the crosswalk.
All three pedestrians were wearing dark clothing, Gill said, and the crosswalk does not have lights or other controlling signals.
Gill said the driver was not arrested or cited, but the full investigation will take some time.
Troopers shut down the southbound lanes of SR-7 while they collected evidence.