Understanding the extent to which youth and families experienced COVID-related stress requires accounting for prior levels of stress and other associated factors. This is especially important for military families, which experience unique stressors and may be reluctant to seek outside help. In this prospective study, we examined the role of pre-pandemic family factors in predicting parent and youth stress during the COVID-19 pandemic. Participants were 234 families with at least one active-duty parent and a 3rd or 5th-grade child. Findings revealed that preexisting factors predicted youth and family COVID-related stress. Specifically, heightened pre-pandemic parental stress and youth internalizing symptoms were significant predictors of COVID-related stress. Implications for mental health professionals and other organizations supporting military parents and families during the COVID-19 pandemic as well as other times of upheaval are discussed. [This is the online version of an article published in "Military Psychology."]