Clint was born to Clinton Eastwood Sr. and Margaret Ruth Runner; the family is of Scottish, Irish, Dutch, and English descent. Eastwood is a descendant of Mayflower passenger and Plymouth Colony Governor, William Bradford. As a child, Eastwood endured the Great Depression, which in turn left its mark on his later films.

Clint Sr., a sometime steel worker in the San Francisco Bay Area, was forced in the 1930s to seek work over a wide area of coastal and inland California. According to film scholar David Kehr, the Eastwoods, with Clint Jr. and sister Jean, spent much of the decade in motion, an experience that would inform such movies as 1982's Honkytonk Man, with its migrant, "Okie" families. 

From his working-class childhood and upbringing, Eastwood the artist drew upon a perspective that was often far more archetypically middle American than those of other California-born actors and directors. When he needed a mid-American backdrop from the 1950s for his 1988 film Bird, Eastwood used the elm-lined streets of central Sacramento, a distinctly un-Hollywood setting that he remembered from living there briefly as a child. 

That leafy cityscape, with its early 20th century clapboard houses, seems worlds removed from the hilly vistas and intellectual pretensions of the Bay Area and from the sun-drenched glitz of Los Angeles, where Clint Jr. would live as a young man.

While attending Oakland Technical High School in Oakland, CA, one of his teachers assigned him a part in a play to try to get him to be less introverted. He did not enjoy the experience.

Eastwood was drafted into the Army, apparently in 1951, during the Korean War. He was sent to Fort Ord on the Monterey Bay, California for basic training. He was supposed to be sent to Korea, but a trip home to Seattle to visit his parents and girlfriend changed that. 

Eastwood caught an uneventful flight home aboard a Navy plane at Moffett Field, but on the return trip aboard a Navy torpedo bomber, the plane developed engine trouble and was forced to make a water landing off San Francisco. He was forced to swim over a mile through the tide to shore. Because of this, instead of being sent to Korea, he was assigned a job as a swimming instructor and remained at Ft. Ord. 

He worked nights and weekends as a bouncer at the NCO club. It was while on duty at Ft. Ord that Eastwood met fellow soldiers and future TV actors Martin Milner ("Route 66" and "Adam-12"), David Janssen ("The Fugitive" and "Harry O"), and Richard Long ("The Big Valley" and "77 Sunset Strip").

After his discharge in 1953, Eastwood moved to Southern California and attended Los Angeles City College, studying drama and business administration under the G.I. Bill.