This study examined sexual identity and birth cohort differences in social support and its association with well-being, using a longitudinal national probability sample of 706 cisgender and non-binary sexual minority individuals from the USA. The data allowed for extensive descriptions of perceived social support and support networks across subgroups. Findings demonstrated that sexual identity and birth cohort differences in overall sizes of support networks and levels of perceived social support were small. Furthermore, fixed effects analyses indicated that changes in the size of respondents’ social support networks were not related to well-being, with a one-person change being associated with a .04 SD change in well-being or less, depending on the indicator of well-being being tested. Moreover, changes in perceived social support were only limitedly related to changes in respondents’ well-being, a 1-point change in the scale of perceived social support being associated with a .11 SD change in life-satisfaction. Associations were smaller for overall well-being or psychological distress, the other two indicators of well-being used. Together, these findings could imply that cross-sectional research has overestimated the relevance of social support for the well-being of sexual minority individuals, but also that general social support is insufficiently tailored to the support needs of the sexual minority population.