Adelphi is an unincorporated area and census-designated place in Prince George's County, Maryland, United States.

[4] Labor organizer Mary Harris "Mother" Jones died in 1930, at the farm of Walter and Lillie May Burgess near Powder Mill and Riggs Roads in present-day Adelphi.

A marker was erected by the Maryland State Highway Administration commemorating Mother Jones at her death site.

Unlike its nearby neighbors Hyattsville and College Park, the area remained relatively undeveloped until immediately following World War II.

To distinguish it from the other neighboring unincorporated communities of Lewisdale and Langley Park, the growing subdivisions banded together in the mid-1950s and adopted the name "Adelphi" to reflect their commitment to the preservation of the historic mill of the same name.

Use of the Adelphi Pool requires paid membership or being accompanied by a member and paying a small fee.

Two notable features of the Adelphi Pool are its long water slide and basketball hoop.

[5] Other adjacent federal facilities include the National Archives at College Park and headquarters of the Food and Drug Administration.

The Prince George's County Police Department serves Adelphi through District 1,[13] with its station in Hyattsville.

Adelphi is served by the Prince George's County Public Schools system.

[21] In 2000, a new elementary school opened in the community dedicated to labor organizer Mary Harris "Mother" Jones.