Jefferson is a census-designated place in Jefferson Parish, Louisiana, United States, on the north side of the Mississippi River. Jefferson is part of the New Orleans–Metairie–Kenner metropolitan statistical area. The population was 11,193 at the 2010 census, and 10,533 in 2020. It is often known by locals as "Old Jefferson", but should not be confused with Old Jefferson in East Baton Rouge Parish, Louisiana.