SACO, a city of the United States, in York county, Maine, on the left or north bank of the Saco river, opposite Biddeford, 9 miles from the sea and 100 from Boston by the Boston and Maine Railroad. The waterpower furnished by the river, which here falls 55 feet, is utilized by various cotton-factories, machine-shops, lumber-mills, Ac. Originally included in Biddeford, but separately incorporated in 1762 as Pepperellborougli, Saco received its present name in 1805 and was made a city in 1867. The population was 5755 in 1870 and 6389 in 1880.