Eagle State is the fictitous state wherein the characters of Desperate Housewives live. It includes the town of Fairview, and the street of Wisteria Lane, 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.
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 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.