Question: What county in Maryland has a town that began as a streetcar suburb northeast of Washington D.C.?
Context: Roland Park is the first planned "suburban" community in North America, located in Baltimore, Maryland.  It was developed between 1890 and 1920 as an upper-class streetcar suburb.  The early phases of the neighborhood were designed by Edward Bouton and Frederick Law Olmsted, Jr. The Mount Rainier Historic District is a national historic district located at Mount Rainier, Prince George's County, Maryland, which began as a streetcar suburb located northeast of Washington, D.C. The district was built on a gently rolling rural landscape from about 1900 to 1940.  The district contains more than 1,000 buildings, which are modestly scaled, detached, single-family, frame houses sited closely together with common setbacks.  It consists primarily of single-family homes, with some small apartment buildings, a few duplexes, and single family homes that include a small storefront, usually located at the corner of an intersection.  With the exception of five churches and a bank building known to have been designed by local architects, the remainder of the district's buildings are vernacular in character.  Some homes contain Queen Anne detailing. Charles Village is a neighborhood located in the north-central area of Baltimore, Maryland, USA.  It is a middle-class area with many single-family homes that is in proximity to many of Baltimore's urban amenities.  The neighborhood began in 1869 when 50 acre of land were purchased for development.  The land was divided and turned over to various builders who constructed home exteriors, leaving the interiors to be custom built according to buyer specifications.  The area was first developed as a streetcar suburb in the early 20th century, and is thought to be the first community to employ tract housing tactics.  At the time, the area was known as "Peabody Heights;" the moniker "Charles Village," derived from Charles Street, the area's major north-south corridor, was coined in the 1970s as the beginning of a process of conceptually grouping a large and somewhat heterogeneous area.  The neighborhood history has been researched and published by Gregory J. Alexander and Paul K. Williams in their book "Charles Village: A Brief History" (The History Press, 2009). Colonial Heights is a neighborhood in the southeast part of the City of Sacramento, California.  An older neighborhood, established in 1910, it makes a fairly typical example of a turn of the century "Streetcar Suburb".  Before cars and buses took over for transportation needs, it was built around the convenient and efficient electric streetcar service provided by the Central California Traction Company. A streetcar suburb is a residential community whose growth and development was strongly shaped by the use of streetcar lines as a primary means of transportation.  Early suburbs were served by horsecars, but by the late 19th century cable cars and electric streetcars, or trams, were used, allowing residences to be built further away from the urban core of a city.  Streetcar suburbs, usually called additions or extensions at the time, were the forerunner of today's suburbs in the United States and Canada.  Western Addition in San Francisco is one of the best example of streetcar suburbs before westward and southward expansion occurred. Mount Rainier is a city in Prince George's County, Maryland, United States. The Lockeland Springs historic neighborhood is a turn-of-the-20th-century streetcar suburb two miles northeast of downtown Nashville, Tennessee in East Nashville.  In 1786, this land was granted by the State of North Carolina to Daniel Williams, in payment for service in the Revolutionary War.  The first house in the area was the log cabin Williams built on the site of the present Lockeland School. The Airview Historic District is a district of 12 houses built between 1896 and 1930 on each side of East Main Street in Middletown, Maryland.  The district was developed to take advantage of the Hagerstown and Frederick Railway, which paralleled what was then known as the National Pike, and is an example of a small-scale streetcar suburb.  The subdivision was subdivided from the Kefauver farm and included a trolley stop in front of developer Lewis Kefauver's house.  The trolley right-of-way is still visible in the deep setback between the street and the sidewalk in the front yards of houses on the north side of the street. The Toronto Hunt Club was established by British Army officers of the Toronto garrison (Fort York) in 1843.  It held gymkhana equestrian events at various sites around the city.  In 1895 it acquired its first permanent home in a rural area east of the city between Kingston Road and the waterfront.  In 1898 the streetcar was extended eastward to the site, and soon the area became a cottage district and then streetcar suburb of Toronto.  This forced the equestrian activities to move further afield.  In 1907 the horses were thus moved to a site in Thornhill (Steeles' Corner at Steeles Avenue and Yonge Street). Ivy Hill Cemetery is a cemetery in the Rosemont Historic District of Alexandria, Virginia, United States.  Burials began at the site in 1811, when it was a family cemetery, and it received a charter as a community cemetery in 1856.  The adjoining residential neighborhood was developed beginning in 1908 as a streetcar suburb of Washington, D.C., as trolley lines of the Washington, Alexandria and Mount Vernon railway extended from Alexandria's nearby Union Station (opened 1905).  The cemetery is now also known for its rare and protected flora and fauna.
Answer: Prince George's County