Many older youth in foster care lack adequate resources and ongoing support in their social networks as they transition into young adulthood, while other youth in these circumstances experience stable social networks providing comprehensive support. Systematically measuring the supportive personal and service-oriented relationships in youth networks expands the scope of inquiry in this area by identifying patterns of social network structure, member composition, and relational qualities that are associated with more or less support provision through formal and informal relationships. These can also be measured over time to observe changes in network form and content and assess network stability. This exploratory study (1) describes the support networks for a small sample of youth with foster care experience who are enrolled in post-secondary education and training programs, (2) assesses changes in these networks over time, and (3) demonstrates the reliability and validity of this methodology for broader use with populations of transition-age foster youth. Findings show that family (biological and foster) and friends are the most prevalent informal supports, relationship ties to parent figures are strongest and provide the most stable and multi-dimensional support, and ties with formal service providers are not as strong, but provide more informational support. The stability of a network ties over time is associated with the breadth of support provided, and network-based social support is associated with post-secondary enrollment at follow-up. Support network profiles are described and interpreted in terms of bonding and bridging social capital. Discussion includes implications for future support network research and guidelines for pre-transition assessment of youth networks in practice.