In the first two decades of the 21st century, scholarly interest in heritage languages (HLs) in the United States has grown significantly. However, despite efforts by language minority families to promote HLs and resist language shifts, relevant research on these efforts and the language practices among the youths in community settings remains limited. In this context, addressing this research gap, the present dissertation investigates a cohort of eight Korean American youths and their parents’ HL maintenance, with a particular focus on youth language practices, language ideologies, and identity dynamics. Using ethnographic case study methods that involved interviews and participant observations, this study explores how Korean American families sustain HL, how their youths engage with HL, and how language ideologies and identities affect Korean American speakers’ practices, particularly in the context lacking ethnic enclaves or public support. The main argument of the present study is that HL maintenance is a complex issue intertwined with conflicting and shifting language ideologies and identities on individual, familial, and community, and societal levels. Despite the undermining impact of conflicting English-dominant ideologies, both families’ significant investments in maintaining Korean, on the one hand, and youths’ agentic HL practices, on the other hand, challenge monolingual and assimilative ideologies, affirming “Koreanness” as central to their identity. Taken together, the findings highlight the critical need for language awareness, societal and institutional support for HLs, as well as innovative pedagogical approaches for young HL learners.