Willow Oak is a census-designated place (CDP) in western Polk County, Florida, United States.

According to the United States Census Bureau, the CDP has a total area of 3.2 square miles (8.3 km2), all land.

As of the census[3] of 2000, there were 4,917 people, 1,784 households, and 1,250 families residing in the CDP.

The racial makeup of the CDP was 83.67% White, 7.02% African American, 0.45% Native American, 0.49% Asian, 0.02% Pacific Islander, 6.45% from other races, and 1.91% from two or more races.

23.8% of all households were made up of individuals, and 4.5% had someone living alone who was 65 years of age or older.