Recent research suggests that the marriage and cohabitation differential in health and well-being depends on whether cohabitors have definite plans to marry or not. We draw on commitment and diffusion perspectives to unpack how marriage plans in the context of cohabiting relationships affect well-being. Using longitudinal data from the Toledo Adolescent Relationships Study, we examined how plans to marry, relationship quality, and economic uncertainty were associated with depressive symptoms among a contemporary sample of young adult cohabitors.  Bivariate analyses showed greater frequency of depressive symptoms for cohabitors without definite plans to marry. Consistent with a diffusion perspective, we found having definite plans to marry was not as influential for depressive symptoms as indicators of relationship dynamics. Further, economic insecurity was associated with higher levels of depressive symptoms. These results add to burgeoning research on the changing nature and function of cohabitation for contemporary young adults.