The Willis Tower, formerly known and still commonly referred to as the Sears Tower, is a 110-story, 1,451-foot (442.3 m) skyscraper in the Loop of Chicago, Illinois, United States. Designed by architect Bruce Graham and engineer Fazlur Rahman Khan of Skidmore, Owings & Merrill (SOM), it opened in 1973 as the world's tallest building, a title that it held for nearly 25 years. It is the third-tallest building in the Western Hemisphere, as well as the 26th-tallest in the world. Each year, more than 1.7 million people visit the Skydeck, the highest observation deck in the United States, making it one of Chicago's most popular tourist destinations. Due to its height and location, the tower is visible from a great distance. The building has appeared in numerous films and television shows set in Chicago.
The building occupies a site bound by Franklin Street, Jackson Boulevard, Wacker Drive, and Adams Street. Graham and Khan designed the building as nine square "tubes", clustered in a 3×3 matrix; seven of the tubes set back at upper floors. The tower has 108 stories as counted by standard methods, though the building's owners count the main roof as 109 and the mechanical penthouse roof as 110. The facade is made of anodized aluminum and black glass. The base of the building contains a retail complex known as the Catalog. The lower half of the tower was originally occupied by retail company Sears, which had its headquarters there until 1994, while the upper stories were rented out.
The structure was known as the Sears Tower from its construction until the naming rights were included in a 2009 lease with the Willis Group. Local area residents still refer to the building by its old name.
As of April 2019, the building's largest tenant is United Airlines, occupying 850,000 square feet (79,000 m2) of space across 16 floors. Other major tenants include ArentFox Schiff, Seyfarth Shaw, Morgan Stanley, and the building's namesake, Willis Towers Watson.
Sears, Roebuck & Co. had occupied an office complex on Chicago's west side since 1906. The existing offices were inadequate by 1966, prompting Sears executives to begin searching for a new site. By 1969, Sears was the largest retailer in the world, with about 350,000 employees. Sears executives quickly determined that a new headquarters complex in the suburbs was infeasible, since it would require relocating about 7,000 employees. Instead, Sears executives decided to consolidate the thousands of employees in offices distributed throughout the Chicago area into one building on the western edge of Chicago's Loop.
Sears asked its outside counsel, Arnstein, Gluck, Weitzenfeld & Minow (now known as Saul Ewing LLP) to suggest a location. The firm consulted with local and federal authorities and the applicable law, then offered Sears two options. The first option was the Goose Island area northwest of the Loop, but Sears's vice president of real estate, Matthew J. Stacom, rejected this proposal. The other was a two-block area in the Loop, bounded by Franklin Street on the east, Jackson Boulevard on the south, Wacker Drive on the west, and Adams Street on the north. Though the site was more centrally located, it was also relatively small, with about 55,000 square feet (5,100 m2). Bernard Feinberg, Albert I. Rubenstein, and Philip Teinowitz had assembled that site over the previous five years, but they had failed to acquire a neighboring 74,000-square-foot (6,900 m2) lot from bus company Greyhound Lines.
Feinberg, Rubenstein, and Teinowitz then bought options for three adjacent lots. Under the terms of each option, unless the three men were able to acquire at least one of the lots within 90 days, all three options would be forfeited. Ultimately, Sears acquired the Loop site in 1970. Sears then obtained permits to close down one block of Quincy Street, which bisected the site from east to west. Attorneys from the Arnstein firm, headed by Andrew Adsit, began buying the properties parcel by parcel. Sears purchased 15 buildings from 100 owners and paid the government of Chicago $2.7 million (equivalent to $22.4 million in 2025) for the block of Quincy Street that was to be closed down.
Sears executives estimated that their new building would need about 4.2 million square feet (390,000 m2), split into 70 stories with 60,000 square feet (5,600 m2) each or 60 stories with 70,000 square feet (6,500 m2) each. Sears commissioned architecture firm Skidmore, Owings & Merrill (SOM) to design the tower. SOM was also the lead structural engineer, and Jaros, Baum & Bolles provided MEP engineering.
Sears planned to move its merchandise group into the building initially, renting out the remaining space to other tenants until needed. Sears executives were accustomed to large floor areas of at least 100,000 square feet (9,300 m2), but SOM architects raised concerns that the large floors would be unattractive to smaller tenants. A subsequent proposal called for two buildings connected by a footbridge, which would respectively contain 50,000 square feet (4,600 m2) and 30,000 square feet (2,800 m2) on each floor, but this was also infeasible.
Some floors were designed with smaller footprints to attract prospective lessees, so the building's height was increased to meet Sears's floor-area requirements. Architect Bruce Graham and structural engineer Fazlur Rahman Khan, both of whom were partners with SOM, proposed a tower with 55,000-square-foot (5,100 m2) floors in the lower part of the building, as well as a series of setbacks with gradually tapering floor plates, giving the tower its distinctive look. During the design process, one of the architects reportedly pulled out nine cigarettes and staggered them vertically until the pair both agreed to the arrangement. This allowed Sears to occupy the large lower stories, while providing more conventional office space that could be rented out on the upper stories. The firm of Saphier, Lerner, Schindler was responsible for determining Sears's space requirements and designing furniture for the company. It conducted a year-long study to determine how 16 of the company's departments should be laid out within the building.
As Sears continued to offer optimistic growth projections, the height of the proposed tower also increased. Under Chicago's relatively lax zoning laws, the site could theoretically accommodate a 300-story building with 13.5 million square feet (1,250,000 m2). In practice, most potential tenants did not want excessively high offices. Additionally, the Federal Aviation Administration (FAA) restricted the height of structures in the area to protect air traffic. FAA officials publicly denied that they had imposed a height limit; however, the area's minimum safe altitude would need to be raised by 1,000 feet (300 m) if the building was just 1 foot (0.30 m) taller. Plans for the tower were announced on July 27, 1970. The 1,450-foot-tall (440 m) building would contain 109 stories as measured from Wacker Drive and 110 stories as measured from Franklin Street. This would make Sears's new tower the tallest in the world, as measured by roof height, although New York City's under-construction World Trade Center Twin Towers would have a taller antenna. Although the Sears Tower would contain 4.4 million square feet (410,000 m2) of space, only about 3.7 million square feet (340,000 m2) would be used as offices.
Work on the building's foundation commenced in August 1970. Contractors excavated the lot to a depth of 50 feet (15 m), and they removed 180,000 cubic feet (5,100 m3) of dirt from the site. By that November, Spencer, White & Prentis Inc. was excavating a trench around the site, measuring 60 feet (18 m) deep and 20 by 216 feet (6.1 by 65.8 m) across. The contractors then built a slurry wall within the trench, made of concrete and reinforced steel. Workers used steel bracing to prevent the slurry wall from collapsing inward, then used caissons to drill 201 holes into the ground. They also rerouted a sewer that had run underneath Quincy Street, which was to be closed permanently as part of the tower's construction.