The Sears Tower, now known as Willis Tower, was constructed from 1970 to 1973. Groundbreaking occurred in August 1970, with construction wrapping up in May 1973 when it became the world's tallest building at the time.

Construction Timeline

Work began with site excavation in August 1970, involving over 2,000 workers who used massive amounts of materials—like enough concrete for a five-mile, eight-lane highway. The structure topped out in May 1973, though some sources note full tenant occupancy and official opening stretched into 1974. By October 1973, the 110-story skyscraper stood at 1,454 feet, reshaping Chicago's skyline.

Key Milestones

  • August 1970 : Groundbreaking and initial excavation, including 50-foot deep digs and rerouting utilities.
  • June 1971 : First steel beam sunk in a ceremony led by Sears chairman Gordon M. Metcaf.
  • May 1973 : Construction completed; final beam signed by 12,000 workers, employees, and locals.
  • 1974 : Fully opened to tenants as Sears headquarters.

Engineering Highlights

Designed by architect Bruce Graham and engineer Fazlur Rahman Khan of Skidmore, Owings & Merrill, the tower's bundled-tube system allowed it to reach unprecedented heights efficiently. It featured 78,000 tons of steel, 25 miles of plumbing, and 1,500 miles of wiring—innovations that set new standards for supertall buildings. At completion, it held the title of tallest building globally for nearly 25 years.

Modern Context

Renamed Willis Tower in 2009, it remains Chicago's iconic landmark with the Skydeck observation deck drawing 1.7 million visitors yearly. As of 2026, no major recent developments alter its 1973 build date, though it celebrated its 50th topping-out anniversary in 2023.

TL;DR: Built 1970-1973, opened fully in 1974.

Information gathered from public forums or data available on the internet and portrayed here.