Derwood is an unincorporated area of about 15,600 people in east-central Montgomery County, Maryland. It is a relatively dense area. It lies just east of Rockville, south east of Gaithersburg, south west of Olney, and north west of the greater Silver Spring, Maryland area. Residents of Derwood have the zip code 20855. The area was originally referred to as "Deer Park" and probably became "Deer Wood" which soon turned into "Derwood.