He remained active in the minor leagues through 1903. He died of pneumonia in 1904, which he contracted during his playing career. Cargo was born in October 1868 in Pittsburgh, Pennsylvania, to Robert and Martha Cargo.
At the 1880 United States Census, Robert Senior worked as a "stockdealer", while Martha was unemployed, with her occupation listed as a "kh".
The family lived in the 11th Ward of Pittsburgh.