Underwood-Petersville is a census-designated place (CDP) in Lauderdale County, Alabama United States.

[4] According to the U.S. Census Bureau, the CDP has a total area of 5.9 square miles (15 km2), all land.

As of the census[6] of 2000, there were 3,137 people, 1,295 households, and 953 families residing in the CDP.

There were 1,378 housing units at an average density of 228.6 per square mile (88.3/km2).

23.2% of all households were made up of individuals, and 9.3% had someone living alone who was 65 years of age or older.

There were 1,506 housing units at an average density of 255.3 per square mile (98.6/km2).

28.4% of all households were made up of individuals, and 10.0% had someone living alone who was 65 years of age or older.