North Dakota, with 887 new cases on both Thursday and Friday, remains the hardest-hit state, based on new cases per capita, followed by South Dakota, Montana and Wisconsin, according to a Reuters tally.
In Tennessee, hospitals in Nashville said they have experienced a 40% increase in patients admitted for Covid-19.
Dr Jeff Pothof, an emergency medicine physician at University of Wisconsin Health in Madison, expressed worry about a lack of compliance with public health measures in the state, where some groups have challenged Democratic governor Tony Evers' Covid-19 restrictions in court.
Chicago mayor Lori Lightfoot announced a curfew on non-essential businesses from 10pm on Friday. She warned residents to avoid social gatherings of more than six people and end all gatherings by 10pm.
Nearly 2,500 people were hospitalised in Illinois, the state’s top public health official, Dr Ngozi Ezike, told a news conference.
The Northeast remains the one region of the county without a significant surge in cases, but infections are trending higher. Boston public schools shifted to online-only learning this week.