Many jurisdictions enacted stay-at-home orders (also called shelter-in-place orders, safer-at-home orders, or lockdowns) when SARS-CoV-2 began spreading in the United States. Based on Google mobility data, every state had substantially fewer visits to transit stations, retail and recreation facilities, workplaces, grocery stores, and pharmacies by the end of March 2020 than in the previous two months. The mean decrease in visitation rates across destination categories was about 30 percent in states without stay-at-home orders and 40 percent in states with stay-at-home orders. Similarly, there were fewer routing requests received by Apple in large cities for public transportation, walking, and driving, with a 10 percentage point greater mean reduction in metropolitan areas under statewide stay-at-home orders. The pandemic led to large decreases in mobility even in states without legal restrictions on travel, but statewide orders were effective public health policy tools for reducing human movement below the level achieved through voluntary behavior change.