Illinois and New York state joined California on Friday in ordering all residents to stay in their homes unless they have vital reasons to go out, restricting the movement of more than 70 million Americans in the most sweeping measures undertaken yet in the U.S. to contain the coronavirus.

The states' governors acted in a bid to fend off the kind of onslaught that has caused the health system in southern Europe to buckle. The lockdowns encompass the three biggest cities in America — New York, Los Angeles and Chicago — as well as No. 8 San Diego and No. 14 San Francisco.

"No, this is not life a...