Old Jamestown is an unincorporated community and census-designated place (CDP) in St. Louis County, Missouri, United States. The population was 19,184 at the 2010 census. Old Jamestown is northwest of the city of St. Louis and borders the Missouri River.

According to the United States Census Bureau, the CDP has a total area of 14.9 square miles (38.7 km), of which 0.008 square miles (0.02 km), or 0.06%, is water. The community is located mostly to the north and west of U.S. Route 67 in northern St. Louis County. West Alton is to the north, across the Missouri River. 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.

Historical population

Census	Pop.	Note	%±
2010	19,184		—
2020	19,790		3.2%
U.S. Decennial Census

Old Jamestown first appeared as a census designated place in the 2010 U.S. Census.

Old Jamestown CDP, Missouri – Racial and ethnic composition
Note: the US Census treats Hispanic/Latino as an ethnic category. This table excludes Latinos from the racial categories and assigns them to a separate category. Hispanics/Latinos may be of any race.

Race / Ethnicity (NH = Non-Hispanic)	Pop 2010	Pop 2020	% 2010	% 2020
White alone (NH)	7,928	4,832	41.33%	24.42%
Black or African American alone (NH)	10,253	13,531	53.45%	68.37%
Native American or Alaska Native alone (NH)	23	26	0.12%	0.13%
Asian alone (NH)	336	307	1.75%	1.55%
Pacific Islander alone (NH)	11	3	0.06%	0.02%
Other race alone (NH)	34	132	0.18%	0.67%
Mixed race or Multiracial (NH)	324	636	1.69%	3.21%
Hispanic or Latino (any race)	275	323	1.43%	1.63%
Total	19,184	19,790	100.00%	100.00%

• Old Jamestown Association website