Although academic and popular interest in consensual nonmonogamy (CNM) is increasing, little is known about the prevalence of CNM. Using two separate U.S. Census based quota samples of single adults in the United States (Study 1: n = 3,905; Study 2: n = 4,813), the present studies show that more than one in five (21.9% in Study 1; 21.2% in Study 2) participants report engaging in CNM at some point in their lifetime. This proportion remained constant across age, education level, income, religion, region, political affiliation, and race, but varied with gender and sexual orientation. Specifically, men (compared to women) and people who identify as gay, lesbian, or bisexual (compared to those who identify as heterosexual) were more likely to report previous engagement in CNM. These findings suggest that a sizable and diverse proportion of U.S. adults have experienced CNM, highlighting the need to incorporate CNM into theoretical and empirical therapy and family science work.