Old Jefferson is a census-designated place (CDP) in East Baton Rouge Parish, Louisiana, United States.

It is part of the Baton Rouge Metropolitan Statistical Area, within the city of St.

[4] According to the United States Census Bureau, the CDP has a total area of 3.5 square miles (9.1 km2), all land.

As of the 2020 United States census, there were 7,339 people, 2,772 households, and 2,021 families residing in the CDP.

Old Jefferson is served by East Baton Rouge Parish Public Schools.