Impact of the COVID-19 pandemic on alcohol and illicit substance use among adults without children, parents, and adolescents was investigated through two studies with five samples from independent ongoing U.S. longitudinal studies. In Study 1, 931 adults without children, parents, and adolescents were surveyed about the pandemic's impact on personal behavior. 19-25% of adults without children, parents, and adolescents reported an increase in alcohol or illicit substance use. In Study 2, 274 adults without children, parents, and adolescents who had been interviewed prior to the pandemic onset about alcohol and illicit substance use problems were re-interviewed after the pandemic's onset to test within-person change. The rate of alcohol or illicit substance use problems increased from pre-pandemic to post-pandemic onset from 13% to 36% among the three groups. Increase in alcohol and illicit substance use problems was positively correlated with increased depression/anxiety and household disruption, suggesting possible mechanisms for increases in substance problems. Findings in both studies held across low- and middle-income families. Findings suggest the need for communitywide policies to increase resources for alcohol and illicit substance use screening and intervention, especially for adolescents.