Md. Code, Land Use § 20–101

(a) There is a Maryland–Washington Regional District.

(b) The regional district consists of:

(1) the entire area of Montgomery County, subject to the limitations in Subtitle 7, Part I of this title and Title 24, Subtitle 2 of this article; and

(2) the entire area of Prince George’s County, except for the City of Laurel as it existed on July 1, 2013.