Total cases Note: The map shows the known locations of coronavirus cases by county. Circles are sized by the number of people there who have tested positive, which may differ from where they contracted the illness. Some people who traveled overseas were taken for treatment in California, Nebraska and Texas. Puerto Rico and the other U.S. territories are not shown. Sources: State and local health agencies, hospitals and C.D.C. Data as of 11:45 p.m. on Friday, March 20.

It started two months ago, just north of Seattle. A young man who had returned from China tested positive for the coronavirus, the first known case in the United States.

At first, the virus was detected only in a handful of cases, and mostly in those who had traveled outside the United States.

There were lone patients in Arizona, in Massachusetts, in Wisconsin. Married couples in Illinois and California were infected. Groups of Americans evacuated from overseas received treatment in California, Nebraska and Texas.

But in the past three weeks, everything has changed. As testing expanded and the virus spread, cases have been confirmed by the dozens, then by the hundreds and thousands.

By Friday night, more than 17,000 cases of the coronavirus had been detected across all 50 states and Washington, D.C., and more than 200 people had died. New York, California and Washington State have been the hardest hit.

Number of New Confirmed Cases Each Day State 123 Total cases New cases each day Date of first case

The climb in the number of cases has been rapid, in part because of more testing. This week saw five times more cases than the previous one, more than 6,000 of which were in New York, which has the most cases in the country.

Change in the Number of New Confirmed Cases The chart shows the percent increase in confirmed cases from March 15 to 20. States with at least 50 cases on March 15 are shown.

See our maps tracking the coronavirus outbreak around the world.