Aon Center (Chicago) the world headquarters of Aon and Amoco. Aon's US operations are still headquartered here. The building is also the co-headquarters of Kraft Heinz. The Standard Oil Building was constructed as the new headquarters of the Standard Oil Company of Indiana, which had previously been housed at South Michigan Avenue and East 9th Street. When it was completed in 1973, it was the tallest building in Chicago and the fourth-tallest in the world, earning it the nickname "Big Stan". (A year later, the Sears Tower took the title as Chicago's and world's tallest.) The building employs a tubular steel-framed structural system
Elgin Tower Building 1999 to showcase its architectural merit. Stickling died later that year, but his benefactors transferred the building to the William R. Stickling Charitable Foundation, who currently maintain the building. An addition was built in 1999 to house, rent-free, the Downtown Neighborhood Association, who intend to revitalize the downtown area. The tower was added to the National Register of Historic Places on May 22, 2002. The Elgin Tower Building is located at 100 E. Chicago St. in Elgin, between Douglas and N. Grove Avenues. This area has historically been known as Fountain Square, generally accepted as the downtown area of Elgin.