Background: Part C of the Individuals with Disabilities Education Act mandates that eligible children under age three receive free access to early intervention (EI) through state-based programs. Despite a robust "Child Find" system, enrollment remains lower than expected. Community and medical professionals often rely on parent report of service utilization to gauge whether children are receiving developmental services. Understanding the reliability of parent report of EI can guide strategies to increase EI participation. Objective: To assess the extent to which parental reports of Part C EI services agree with state-based service records. Method: We address this research objective among 162 children and their parents from marginalized communities in Boston, MA and New Haven, CT who were identified as having a higher likelihood of autism and participated in a randomized controlled trial to facilitate access to autism evaluation and treatment. Parents reported whether their child was currently receiving EI services at four time points and released their child's EI service records from state agencies. Results: Overall agreement between parent and service records was 70% and ranged from fair to moderate and service-specific agreement ranged from 46% to 81.6%. Sensitivity, specificity, and positive/negative predictive values ranged widely for both overall and service-specific EI use. We found no differences in agreement by sociodemographic characteristics, but agreement was higher when children received EI services at home. Conclusions: Our findings support community and medical professionals' elicitation of children's EI service use from parents, especially for participation in EI overall and for physical and occupational therapy.