Cairo, city in extreme southern Illinois, at the convergence of the Ohio and Mississippi rivers. Cairo is the seat of Alexander County. Located in a cotton-growing region, the city is a shipping and trade center. It was named for its supposed geographic similarity to the setting of Cairo, Egypt. Founded by white settlers in 1837 and incorporated in 1857, Cairo profited by the coming of the railroad in 1855 and as a major Union supply base during the American Civil War (1861-1865). Its economy subsequently declined. Population 5,931 (1980); 4,846 (1990); 3,632 (2000).
