The 2020 census already was destined to be an even more daunting venture — the first ever conducted mostly online, in a deeply polarized nation where mistrust of the government and immigrants fearful of authorities could make an accurate count harder than in recent memory.

The coronavirus outbreak adds new layers of uncertainty, beginning with the efforts by thousands of civic groups and local governments to persuade their residents just to fill out the census form. This week the leaders of the Detroit 2020 census campaign, one of the nation’s most innovative efforts to boost census response, canceled a kickoff rally that was set for Monday at a local high school.

“We were planning to have 700 people there, passing out materials,” said Victoria Kovari, the campaign’s executive director. “We ordered thousands of posters for local businesses; we ordered cards. And we found out yesterday they closed the local schools.”

In Columbus, Ohio, a statewide campaign by civic and philanthropic groups to boost response has hit similar headwinds. “This morning I was supposed to meet with 99 Head Start directors,” said Tracy Nájera, the co-leader of the Ohio Census Advocacy Coalition, “and yesterday afternoon I got a call that the meeting would be much smaller, close to 40.

“I got to the session this morning, and there were eight. So it’s having a real and immediate impact.”

Both women said their groups are revising months of plans on the fly, canceling community events, shifting messages to social media and holding staff meetings by videoconference. The Ohio campaign, which had used grant money to plan town halls, block parties and other census-promotion events with 45 grass-roots groups, now must search for ways to get the message out without drawing crowds.