San Marco is a neighborhood of Jacksonville, Florida, south of Downtown across the St. Johns River. The neighborhood was formerly the independent city of South Jacksonville until it was annexed by Jacksonville in 1932. The neighborhood is primarily residential, with an integrated commercial sector known as San Marco Square.

There are more than 500 neighborhoods within the area of Jacksonville, Florida, the largest city in the contiguous United States by area. These include Downtown Jacksonville and surrounding neighborhoods. Additionally, greater Jacksonville is traditionally divided into several major sections with amorphous boundaries: Northside, Westside, Southside, and Arlington, as well as the Jacksonville Beaches.