Fleming Island is an unincorporated community and census-designated place (CDP) in Clay County, Florida, United States.

[2] It is located 21 miles (34 km) southwest of downtown Jacksonville, on the western side of the St. Johns River, off US 17.

[4] In 1942, when the area was undeveloped, the U.S. Navy constructed four asphalt runways on the site and established a Naval Outlying Field designated as NOLF Fleming Island, an auxiliary airfield to Naval Air Station Jacksonville.

[5] The Navy abandoned the auxiliary airfield in the 1960s, its runways too short to accommodate the jet aircraft then in operation at nearby NAS Jacksonville and NAS Cecil Field, and in the late 1990s the decaying runways were demolished to make way for current residential development.

[8] There is an 8-foot-wide (2.4 m) sidewalk running the length of Fleming Island, providing about 7 miles (11 km) of walking, jogging and biking.

Moccasin Slough also features a canal navigable by canoe or small boat, dug almost all the way to Doctors Lake.

Fleming Island has relatively low crime and consistently scores high in livability.

The Fleming Island CDP is located in northeastern Clay County, sharing its northern border with the southern town limits of Orange Park.

Some locals favor opening this to Black Creek but so far, the St. Johns Water Management District has not pursued the idea of doing this.