Background: Community participation and systematic follow-up of children who miss vaccination appointments are central to sustaining routine immunization. This study assessed community-engagement and defaulter-tracking practices in facilities in Benin City, Nigeria, and explored stakeholder perspectives on how these practices supported uptake. Methods: A cross-sectional mixed-methods study was conducted from April 2023 to October 2024. A proportionately allocated sample of 112 routine-immunization facilities was selected across Oredo, Egor and Ikpoba-Okha Local Government Areas. Practices were assessed with a supportive-supervision checklist. Fifteen purposively selected programme managers, facility focal persons and community stakeholders participated in key-informant interviews. Descriptive statistics and thematic analysis were used. Coverage estimates from the parent survey of 620 children aged 12-23 months described the programme context. Results: Most facilities registered children by settlement, conducted defaulter tracking, involved communities in organizing sessions and reported functional village development committees. Reconciliation meetings were less consistent. Tracking depended mainly on tickler boxes and routine-immunization registers, while few facilities reported mobilizer-assisted tracking. Stakeholders described town announcers, religious institutions, youth leaders and community meetings as channels for mobilization, trust building and outreach. Completion declined when the second measles-containing vaccine dose was considered. Conclusion: Community linkage and defaulter tracking were substantial, but tracking remained largely facility based. Programmes should connect register-based identification with named community actors, documented referral and feedback pathways, regular reconciliation meetings and monitoring of successful return to vaccination.