Detailed Methodology and Sources: COVID-19 Data

This interactive feature aggregates data from the Centers for Disease Control and Prevention (CDC), state- and local-level public health agencies. County-level data is confirmed by referencing state and local agencies directly. Cases, deaths, and per capita adjustments reflect cumulative totals since January 22, 2020.

For most states, USAFacts directly collects the daily county-level cumulative totals of positive cases and deaths from a table, dashboard, or PDF on the state public health website. This data is compiled either through scraping or manual entry.

Because of the frequency with which we are currently updating this data, they may not reflect the exact numbers reported state and local government organizations or the news media. Numbers may also fluctuate as agencies update their own data. At present, USAFacts is working on ensuring this data uses the most up-to-date information possible.

Unique states

California and Texas state public health websites do not currently offer accurate county-level statistics. Instead, USAFacts individually pulls the most current numbers from each county’s public health website (58 counties for California and 254 counties for Texas).

Rhode Island’s public health website reports by town rather than the county, and we currently roll this up into counties. Rhode Island also doesn't report towns or counties with respect to its deaths, however, the state does periodically provide data on deaths in nursing homes, providing the location for those.

The Kansas state public health agency updates its data on Mondays, Wednesdays, and Fridays. The case and death counts for Kansas counties are compiled by consulting both the state data and county public health agency data, where available. If the two sources are not reporting the same values, the higher value is recorded.

Utah’s state government groups 22 of the state's 29 counties into one of six regional health agencies. Data for these individual counties is compiled from the six regional agencies.

Idaho's state health agency does not update its data on Sundays.

Cases not attributed to specific counties

The 21 cases confirmed on the Grand Princess cruise ship on March 5 and 6 are attributed to the state of California, but not to any counties.

USAFacts attempts to match each case with a county, but some cases counted at the state level are not allocated to counties due to lack of information.

Counting cases and deaths

USAFacts currently counts presumptive positive cases as confirmed cases, as this is in line with how the CDC reports data. We assign cases to where the person was diagnosed as that information becomes available.

USAFacts takes deaths directly from state and local agencies. Per official CDC reporting guidelines, deaths should only be counted as COVID-19-related if the virus played a direct role in causing death. This means coronavirus can be one of several causes of death, such as if a person passes away from having both pneumonia and COVID-19. It does not mean that anyone who has COVID-19 and dies is automatically considered a COVID-19 death.

If a state reports both the location of death and the location of residency, we attribute the death to the location of residency.

Daily and weekly metrics are based on calculated differences in cumulative cases reported by states. Not all states report on the same day or for the same amount of days. States revise current and historic cases numbers for various reasons. We adjust cumulative counts by consulting a state's historical data, when possible. Our daily or 7-day calculations can result in negative numbers if states revise case numbers without providing historical data. We've refined our process since beginning this project and revise older reported numbers to ensure the data doesn't show decreasing cases. The logic behind this is that the number of confirmed cases cannot decrease in a given location.

Timing

States and counties release data at various points throughout the day, with some localities updating data multiple times daily or even continuously. For USAFacts' data to be as current as possible, we mostly collect data in the evening (Pacific Time). We generally update the data on our website by 9am PST.

Entry Process and Validation

Our entry process is partially manual but automated where possible. This data is continually validated and checked by the USAFacts team.