Costner was born in Lynwood, California, the youngest of the three sons (the middle of whom died at birth) of Sharon Rae (née Tedrick), a welfare worker, and William Costner, an electrician and later utilities executive. He has German, Irish and Cherokee ancestry (his Oklahoma-born paternal grandfather was half Cherokee). Costner was raised Baptist. He attended elementary school at McKevette School, in Santa Paula, California, Cabrillo Jr. High School and Buena High in Ventura, California. A poor student, Costner enjoyed sports in spite of his slight stature and took piano lessons, wrote poetry and sang in the First Baptist Choir.

Spending his teenage years in various parts of California as his father's career progressed, Costner lived in Orange County, then in Visalia (Tulare County), attending Mt. Whitney High School, and graduated from Villa Park High School in Villa Park, California, in 1973. He went on to earn a B.A. in business from California State University, Fullerto