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.[8] During his term, he served on the Banking, Finance and Urban Affairs Committee; Government Operations Committee; Financial Institutions Supervision, Regulation and Insurance Subcommittee; Housing and Community Development Subcommittee; and Government Information, Justice and Agriculture Subcommittee
[3]
During the Republican-led[9] 1991 decennial redistricting, the 16th district added portions of staunchly Republican McHenry County. Donald Manzullo defeated Cox in the newly drawn 16th district.[10] At the time of Cox's loss, fellow Illinois Democrat Dan Rostenkowski was laying the groundwork to get Cox a seat on the United States House Committee on Ways and Means.[11] Manzullo held the seat until his defeat by fellow Republican Congressman Adam Kinzinger for renomination in the 2012 Republican primary election held on March 20, 2012, after the 2011 decennial redistricting.[12][13]
Post congressional career
Following his term, Cox returned to Galena, Illinois where he continued his private law practice. Since returning to Galena, Cox he served as City Attorney for the City of Galena, Illinois.[14] Cox served as Vice President for External Affairs and General Counsel for Jo-Carroll Energy, Inc. (NFP), an Illinois energy cooperative until he retired.