Linthicum is a census-designated place and unincorporated community in Anne Arundel County, Maryland, United States. The population was 10,324 at the 2010 census. It is located directly north of Baltimore-Washington International Thurgood Marshall Airport.Designated as "Linthicum Heights" and zip code 21090 by the US Postal Service, Linthicum has been traditionally divided into two distinct communities each with its own community association and identity. These two communities, split by the Baltimore Beltway in 1957, are Linthicum and North Linthicum Both communities developed as a result of their locations adjacent to the Baltimore and Annapolis Short Line railroad which brought commuters to the original truck farming community.As a developed community, Linthicum began with the 1908 founding of the "Linthicum Heights Company", though a "Linthicum" or "Linthicum's" station on the 1887 Annapolis and Baltimore Short Line railroad existed at least as early as 1889.