This study examined the extent to which socially structured factors impact adults' participation in undergraduate programmes in the USA. In a collective sense, this study started with an assumption that adults' decision to participate in educational programmes does not only rely on individual psychological and their adjacent environmental attributes, but it is also, in part, influenced by socially structured contexts surrounding them. Using the state as a unit of analysis, this study analysed the relationships between socio-demographic, economic, educational and political factors and the variation of adults' participation in the undergraduate programmes. Variables from both educational and socio-demographic factors had stronger relationships with adults' participation. Some variables that states can control through policy-related actions were meaningfully associated with adults' participation. Through this sociological understanding of adult participation in higher education, this study will supplement the lack of attention to macro-level perspectives in participation research in adult education.