[3] In 1976, Cox defeated Victor Sprengelmeyer, a Republican appointee, for election to serve as State's Attorney for Jo Daviess County, Illinois.

[4][5] During his tenure as State's Attorney, Cox was an advocate for enhanced federal prosecution of human traffickers operating on the Illinois—Iowa border.

[5] After the retirement of Republican incumbent Lynn Morley Martin, Cox joined the race to succeed her in Congress.

Surprisingly, Cox defeated Republican John Hallock, a member of the Illinois House of Representatives from Rockford.

[12][13] Following his term, Cox returned to Galena, Illinois where he continued his private law practice.