Prince George's County (often shortened to PG County, PG, or PGC) is located in the U.S. state of Maryland bordering the eastern portion of Washington, D.C. As of the 2020 U.S. census, the population was 967,201, making it the second-most populous county in Maryland, behind neighboring Montgomery County. The 2020 census counted an increase of nearly 104,000 in the previous ten years. Its county seat is Upper Marlboro. It is the most populous African American-majority county in the United States, as well as the second most affluent behind neighboring Charles County.

The county is part of the Capital region of the state, though portions of the county are considered to be in Southern Maryland. The county also hosts many federal governmental facilities, such as Joint Base Andrews and the United States Census Bureau headquarters.

The official name of the county, as specified in the county's charter, is "Prince George's County, Maryland". The county is named after Prince George of Denmark (1653–1708), the consort of Anne, Queen of Great Britain, and the brother of King Christian V of Denmark and Norway. The county's demonym is Prince Georgian, and its motto is Semper Eadem (English: "Ever the Same"), a phrase used by Queen Anne. Prince George's County is frequently referred to as "PG" or "PG County", an abbreviation which is the subject of debate, some residents viewing it as a pejorative and others holding neutral feelings toward the term or even preferring the abbreviation over the full name.

The Cretaceous Era brought dinosaurs to the area that left fossils now preserved in a 7.5-acre (3.0 ha) park in Laurel. The site, which among other finds has yielded fossilized teeth from Astrodon and Priconodon species, has been called the most prolific in the eastern United States.

In the mid to late Holocene era, the area was occupied by Paleo-Native Americans and then, later, Native Americans. When the first European settlers arrived, what is now Prince George's County was inhabited by people of the Piscataway Indian Nation. Three branches of the tribe are still living today, two of which are headquartered in Prince George's County.

Prince George's County was created by the English Council of Maryland in the Province of Maryland in April 1696 from portions of Charles and Calvert counties. The county was divided into six districts referred to as "Hundreds": Mattapany, Petuxant, Collington, Mount Calvert, Piscattoway and New Scotland.

A portion was detached in 1748 to form Frederick County. Because Frederick County was subsequently divided to form the present Allegany, Garrett, Montgomery, and Washington counties, all of these counties in addition were derived from what had up to 1748 been Prince George's County.

In 1791, portions of Prince George's County were ceded to form the new District of Columbia (along with portions of Montgomery County, Maryland and parts of Northern Virginia that were later returned to Virginia).