He has described himself as a 'momma's boy' and not 'the most popular kid' during his school years. He attended this school at the same time as Jason Momoa, who would also later become an actor in DC Superhero films. Routh attended Norwalk High School, where he played sports, and participated in music and theatre. In his spare time, he played the trumpet and the piano. During his childhood, Routh thought a full-time acting career was unrealistic, citing his small-town background. Routh grew up in Norwalk, approximately 100 miles (160 km) south of Woolstock, the birthplace of George Reeves, the first actor to play Superman on television.
Routh was raised in a Methodist family, and has English, Scottish, German, and Dutch ancestry.
Routh, the third of four children, was born in Des Moines, Iowa, to Catherine LaVaughn (née Lear), a teacher, and Ronald Ray Routh, a carpenter.