Cabin John is a census-designated place and an unincorporated area in Montgomery County, Maryland, United States.
Early land records in 1715 cite Captain John's Run, now Cabin John Creek. The toponym "Cabin John" is thought to be a corruption of the name "Captain John", but the origin of the name remains unresolved.
As an unincorporated area, Cabin John's boundaries are not officially defined. Cabin John is, however, recognized by the United States Census Bureau as a census-designated place, and by the United States Geological Survey as a populated place located at 38°58′30″N 77°9′33″W (38.975110, −77.159281). The borders are roughly defined as the area of land outlined by the Capital Beltway, Cabin John Parkway, and the Clara Barton Parkway.
According to the United States Census Bureau, the place has a total area of 1.3 square miles (3.4 km2), of which 1.0 square mile (2.6 km2) is land and 0.3 square miles (0.78 km2) (25.56%) is water.
At the 2000 census there were 1,734 people, 668 households, and 464 families residing in the area. The population density was 1,762.4 people per square mile (683.2/km2). There were 688 housing units at an average density of 699.3/sq mi (271.1/km2). The racial makeup of the area was 85.01% White, 3.63% African American, 0.23% Native American, 8.77% Asian, 0.46% from other races, and 1.90% from two or more races.