Which federal building located in the Federal Plaza also serves as a courthouse?

The Everett McKinley Dirksen Courthouse serves as a federal courthouse and is located within the Federal Plaza in Chicago. This building is significant for its role in the judicial system, housing several courtrooms and judicial offices. It is named after Everett McKinley Dirksen, a prominent U.S. Senator from Illinois, and reflects the federal architectural style typical of the mid-20th century.

In contrast, while the Richard J. Daley Center is a major civic building in Chicago, it primarily serves as a center for local government operations and does not function as a federal courthouse. The James R. Thompson Center houses state government offices and is known for its distinctive postmodern architecture but does not host federal court functions. Lastly, the Chicago Cultural Center is mainly focused on the arts and cultural programs and does not serve any judicial purposes. Therefore, the Dirksen Courthouse is the correct answer because it uniquely fulfills the dual role of being a federal building and a courthouse.