Protesters in Maryland joined others in state capitals such as Austin, Texas, and Carson City, Nevada.
The order takes effect at 8 p.m. Monday night.
In a sprint session, the General Assembly approved legislation to aid with coronavirus response, make hate crimes easier to prosecute, require University System of Maryland institutions to create outbreak response laws, and more.
The announcement comes as the governor closed the state's casinos, racetracks and simulcast betting facilities indefinitely.
Maryland had confirmed 12 cases of COVID-19 as of Thursday afternoon.
“I don’t see any other way to get the facts,” he said.
He's launching a national nonprofit organization.