Old Jamestown is an unincorporated community and census-designated place (CDP) in St. Louis County, Missouri, United States.

[4] Old Jamestown is northwest of the city of St. Louis and borders the Missouri River.

[4] The community is located mostly to the north and west of U.S. Route 67 in northern St. Louis County.

Florissant is to the southwest, and Black Jack and Spanish Lake are to the south.

The CDP is located 17 miles (27 km) north of downtown St. Louis.