Source: U.S. Census Bureau
Data for "Resident Population" are estimates as of July 1. Data for 1970, 1980, 1990, and 2000 are annual census.
Population estimates are updated annually using current data on births, deaths, and migration to calculate population change since the most recent decennial census. The annual time series of estimates begins with the most recent decennial census data and extends to the vintage year. Each vintage of estimates includes all years since the most recent decennial census.
U.S. Census Bureau, Resident Population in Petroleum County, MT [MTPETR9POP], retrieved from FRED, Federal Reserve Bank of St. Louis; https://fred.stlouisfed.org/series/MTPETR9POP, May 17, 2022.