Robert Rathbun Wilson was born in Frontier, Wyoming, in 1914, the son of Platt Elvin and Edith Elizabeth (Rathbun) Wilson. He had an older sister, Mary Jane. His parents separated when he was eight years old, and custody was awarded to his father, although he lived with his mother from time to time. Much of his early life was spent on cattle ranches. He changed schools frequently, and attended a number of schools, including the Todd School in Woodstock, Illinois, where his grandmother worked.