The New York Times is releasing a series of data files with cumulative counts of coronavirus cases in the United States, at the state and county level, over time.The data begins with the first reported coronavirus case in Washington State on Jan. 21, 2020.

The data is the product of dozens of journalists working across several time zones to monitor news conferences, analyze data releases and seek clarification from public officials on how they categorize cases.

Confirmed cases are patients who test positive for the coronavirus. A case is consider confirmed when it is reported by a federal, state, territorial or local government agency.

For each date, there is the cumulative number of confirmed cases and deaths available as reported that day in that county or state. All cases and deaths are counted on the date they are first announced.

In some instances, the data is reported from multiple counties or other non-county geographies as a single county. For instance, there is a single value for New York City, comprising the cases for New York, Kings, Queens, Bronx and Richmond Counties.

Cities like St. Louis and Baltimore that are administered separately from an adjacent county of the same name are counted separately.

Many state health departments choose to report cases separately when the patient's county of residence is unknown or pending determination. In these instances, the county name is recorded as 'Unknown' As more information about these cases becomes available, the cumulative number of cases in 'Unknown' counties may fluctuate.

Sometimes, cases are first reported in one county and then moved to another county. As a result, the cumulative number of cases may change for a given county.

All cases for the five boroughs of New York City (New York, Kings, Queens, Bronx and Richmond counties) are assigned to a single area called New York City. There is a large jump in the number of deaths on April 6th due to switching from data from New York City to data from New York state for deaths.

For all New York state counties, starting on April 8th the New York Times is reporting deaths by place of fatality instead of residence of individual.

Starting April 12th, the New York Times case count excludes cases labeled by the state as 'Non-Georgia Resident' leading to a one day drop in cases. These cases were previously included as cases with 'Unknown' county.

Four counties (Cass, Clay, Jackson and Platte) overlap the municipality of Kansas City, Mo. The cases and deaths for these four counties are only shown for the portions exclusive of Kansas City. Cases and deaths for Kansas City are reported as their own line.

Counts for Alameda County include cases and deaths from Berkeley and the Grand Princess cruise ship.

Counts for Douglas County include cases brought to the state from the Diamond Princess cruise ship.

All cases and deaths for Chicago are reported as part of Cook County.

Counts for Guam include cases reported from the USS Theodore Roosevelt.