Here is the complaint in Cheyenne River Sioux Tribe v. Donald J. Trump, which relates to Cheyenne River’s Health Safety Checkpoints.

From the complaint:

The United States and the nation’s Native American tribes are in a state of emergency. COVID-19 is spreading rapidly throughout the country, infecting millions of people, including in South Dakota, which has had 6,353 confirmed cases and 83 deaths outside the boundaries of the Cheyenne River Sioux Reservation. Experts estimate that, for every confirmed COVID-19 case, there could be as many as eleven unconfirmed cases. “At this time, there is no known cure, no effective treatment, and no vaccine. Because people may be infected but asymptomatic, they may unwittingly infect others.” S. Bay United Pentecostal Church v. Newsom, 590 U.S. —-, 140 S. Ct. 1613, 2020 WL 2813056 at *1 (May 29, 2020) (Roberts, C.J., concurring).

On April 2, 2020, in direct response to the COVID-19 pandemic, the Cheyenne River Sioux Tribe established a comprehensive COVID-19 response plan, including Health Safety checkpoints to monitor the entry of individuals onto the Tribe’s Reservation. These Health Safety Checkpoints have allowed the Tribe to effectively track individuals that have returned to the Reservation from hotspots throughout both the state of South Dakota and other off-Reservation locations and to keep the Tribe’s rate of infection significantly below the rate for South Dakota at large. To date, the Tribe has had no COVID-19 deaths.

News coverage here, and the press release can be seen here.