The 2020 coronavirus pandemic was associated with a substantial increase in time spent alone. This paper uses US time-diary data to examine the extent to which changes in activities were associated with increases in time alone and to what extent time alone increased within activities, and also examines the effect of pandemic severity and government policies. Increases in work at home were a substantial contributor to the increase in time spent alone, although increases in time alone at the workplace also played a role. Reallocation of leisure toward fewer social activities was another contributor. Higher state Covid rates increased time alone for single-person households, while government policies did little. There is some evidence that increases in time alone were associated with increases in activities that are substitute for social activity.