Opilka, a native of St. Louis, was the Blues' fifth round selection (146th overall) at the 2015 National Hockey League (NHL) Entry Draft.
Opilka, 18, has spent the past two seasons in the U.S. National Team Development Program (USNTDP). In 2014-15, he made 33 appearances with the U-18 club in the United States Hockey League (USHL), recording a 2.70 goals against average, a .888 save percentage and three shutouts.
In 2013-14, the 6-foot-1, 192-pound goaltender logged a 3.59 goals-against average and a .863 save percentage in 30 games with the USNTDP's U-17 club.
Internationally, Opilka earned a gold medal with Team USA at both the 2015 U-18 World Juniors and the 2014 U-17 World Hockey Championships.