Windsor Ruins is an antebellum mansion located near Port Gibson, Mississippi. The estate was built in 1861 by Smith Coffee Daniell II, a wealthy cotton planter who owned a plantation land of 21,000 acres in Louisiana and Mississippi. The mansion had 23 rooms, an above-ground basement, two residential floors, and an attic. Greek Revival, Italianate, and Gothic styles influenced the mansion's architecture. The mansion's ell-shaped extension contained the kitchen, pantry, and dining room. The mansion also had rainwater storage tanks in the attic, which supplied water to two bathrooms. A dome, which provided a view of the Mississippi River, was centred on top of the roof.

However, Daniell died in April 1861, just weeks after completing his mansion. During the Civil War, much of the family's holdings were lost. After the war, the estate survived but was destroyed by an accidental fire on February 17, 1890. The only surviving parts of the mansion were the columns and ironwork. One flight of metal stairs from Windsor was installed at Oakland Chapel on the campus of nearby Alcorn State University. Unfortunately, all of the Daniell family's photographs and drawings of the mansion were lost in the fire.

The Mississippi Department of Archives and History now administers Windsor Ruins. Descendants of the Daniell family donated Windsor Ruins to the State of Mississippi in 1974. The site was listed on the National Register of Historic Places in 1971. In 1991, historians discovered a drawing of Windsor sketched in 1863 by a Union soldier in Major General Ulysses S. Grant's army. The soldier's picture is similar to the illustration reproduced in some sources. The site is a popular tourist destination and attracts visitors interested in history and architecture.