Robert Cary Long, Jr. (1810–1849) was the son of a late 18th Century - early 19th Century famous architect Robert Cary Long, Sr. in Baltimore, Maryland and also himself, a well-known 19th Century architect who also practiced in Baltimore. His works in the city included Old St. Paul's Episcopal Church (Third Building, 1812), St. Peter the Apostle Church, Mount Calvary Church (Episcopal/Anglican/now Roman Catholic), the Lloyd Street Synagogue, and many other buildings in central Maryland.
Also known as a well-known local architect, Robert Cary Long, Sr., younger Long's father also assisted in the construction of the famous iconic old "Assembly Rooms" building which was designed by local landowner Col. Lloyd Nicholas Rogers of "Druid Hill" mansion in 1797. Sited on the northeast corner of Holliday and East Fayette Streets, of Georgian/Federal styled architecture, used for the Baltimore Dancing Assembly with their frequent receptions, dances, social events and soirees along with various intellectuctual and cultural events.