Bill's business career began at age 19 when he and his younger brother co-founded Electronic Theatre Controls, Inc., a company that now manufactures over half of the theater lighting equipment in the United States.

Before he became a Member of Congress, Bill worked as a high-energy physicist and particle accelerator designer at Fermi National Accelerator Laboratory (Fermilab). He was a member of the team that discovered the top quark, the heaviest known form of matter. He also led the teams that designed and built several scientific facilities and detectors still in use today, including the Recycler Ring, the latest of Fermilab's giant particle accelerators. Bill lives in Naperville with his wife Aesook, who is also a physicist. Bill has two grown children, Billy and Christine. Bill's father was a civil rights lawyer who wrote much of the enforcement language behind the Civil Rights Act of 1964.