Background: Utilization of child health services through routine visits to community health posts (Posyandu) is essential for growth monitoring, immunization, and disease prevention among toddlers. However, utilization remains influenced by a range of biological, psychological, social, and environmental factors. Understanding these determinants is important for developing effective community-based interventions. This study aimed to analyze the biopsychosocial and household environmental determinants of toddler health service utilization in Kediri City, Indonesia. Methods: A cross-sectional study was conducted among 515 toddlers selected through random sampling. Data were collected through a validated and reliable structured questionnaire administered to mothers of toddlers. The outcome variable was toddler health service utilization through Posyandu visits, while the predictor variables included biological, psychological, social, and household environmental factors. Data were analyzed using chi-square tests and multivariable logistic regression. Results: Most toddlers (78.8%) attended Posyandu routinely. Bivariate analysis showed significant associations between toddler health service utilization and most biological, psychological, social, and household environmental factors (p < 0.05). In the multivariable model, paternal education, antenatal care history, parity, BPJS enrollment, access to health information, housing density, home ventilation, floor type, wall type, waste management, exposure to cigarette smoke, and access to clean water remained significant predictors of Posyandu utilization. BPJS enrollment was the strongest determinant (AOR = 8.076; p < 0.001). Conclusion: Toddler health service utilization is influenced by multiple biopsychosocial and environmental factors. Strengthening health insurance coverage, improving access to health information, and promoting healthy household environments may contribute to increased utilization of Posyandu services.