Purpose The aim of the study was to document mental health service use (counseling and medication) among youth in foster care, examine how prepared they feel to manage their mental health, and investigate predictors of service use and preparedness. Methods The study includes a representative sample of youth in California foster care at age 17 years who participated in in-person, structured interviews (n = 727). Survey measures captured youth characteristics, their mental health service use, and their level of preparedness to manage their mental health. Data from a child welfare worker survey were used to capture county-level service availability, helpfulness, and coordination. Binary and ordered logistic regression were used to predict mental health service use and preparedness. Results Youth reported high rates of mental health service use and one-fifth of the sample reported feeling less than prepared to manage their mental health. Youth who screened positive for mental disorders were less prepared than their peers to manage their mental health. Physical (odds ratio [OR] = 1.44; p < .05) and sexual abuse (OR = 2.04; p < .001) predicted past year use of counseling. Sexual abuse also predicted medication use (OR = 1.97; p < .01). Youth who identified as 100% heterosexual were less likely than non-100% heterosexual peers to use counseling (OR = .58; p < .05). The results also suggest geographic variation in use. Finally, caseworkers' perception of greater helpfulness of services in the county they worked predicted greater mental health preparedness (OR = 1.23; p < .05). Conclusions Mental health service use remains high among youth in foster care. Youth with particular characteristics may benefit from interventions aimed at preparing them for managing their mental health in adulthood.