Improved therapeutics and supportive care in hospitals have helped reduce mortality from COVID-19. However, there is limited evidence as to whether nursing home residents, who account for a disproportionate share of COVID-19 deaths and are often managed conservatively in the nursing home instead of being admitted to the hospital, have experienced similar mortality reductions. In this study we examined changes in thirty-day mortality rates between March and November 2020 among 12,271 nursing home residents with COVID-19. We found that adjusted mortality rates significantly declined from a high of 20.9 percent in early April to 11.2 percent in early November. Mortality risk declined for residents with both symptomatic and asymptomatic infections and for residents with both high and low clinical complexity. The mechanisms driving these trends are not entirely understood, but they may include improved clinical management within nursing homes, improved personal protective equipment supply and use, and genetic changes in the virus.