Eagle State is the fictitious state wherein the characters of Desperate Housewives live. It includes the town of Fairview, and the street of Wisteria Lane, the stage of the main events of the series. Although it is a fictitious state, the characters often refer to other states in the U.S.A. that are indeed real, such as Maryland or Utah.
There is a seal behind the judge's chair in the courtroom in season 8 that has the date 1876 so it is believed that The Eagle State was founded in 1876, 100 years after the founding of the United States. Colorado was founded in 1876. The state flag is also seen in the courtroom to the left of the Seal. The flag features a solid dark blue background with the state seal in the center.
Eagle State's location is not certain since there are some facts that don't match. In episode 2x15, "Thank You So Much", Susan notes that she threw her wedding ring from her marriage to Karl out the window on Rt. 7. A sign is later seen bearing the US-7 route, which is a highway that runs north-south between Connecticut and Vermont. That would imply that Eagle State belongs to the North East region, near the Canadian border. But in episode 2x12, when Bree drops Andrew on the side of the road, mountains are clearly seen in the background, which could potentially be in the North East but matches better to the Rocky Mountains, near Colorado. In 6x12, "You Gotta Get a Gimmick," after Karl's death, Julie decides to take the money Karl left her and visit her cousins "back East," which would imply they leave somewhere near the West coast, which would justify a warm Christmas.