The crash took place on Highway 50 near the city airport just before 10 a.m. when the car was traveling eastbound and it struck into the semi, which was attempting to turn onto Highway 231.
The semi was driving slowly when the Cadillac rear-ended it.
The adults in the car were not using seatbelts and the child was not properly restrained.
The two adults in the car were pronounced dead at the scene.
They have been identified as Jeremy Jaramillo, 29, and Brittany Montez, 31.
Jaramillo was the driver of the vehicle.
The 1-year-old suffered life-threatening injuries and was flown to Children’s Hospital in Colorado Springs.
The truck driver was not injured.
Colorado State Patrol was investigating the crash.