Background: Measles elimination requires ≥95% vaccination coverage, yet coverage remains low in many Nigerian states. Socioeconomic disparities in vaccination are well documented nationally, but evidence from the South-South zone is limited. This study assessed measles vaccination coverage, socioeconomic disparities, and outbreak risk in Rivers State, Nigeria. Methods: A community-based cross-sectional study enrolled 1,152 children aged 12-23 months from 60 wards across 15 local government areas (LGAs) using multi-stage stratified cluster sampling. Measles-containing vaccine first- and second-dose (MCV1 and MCV2) coverage was verified by immunization card or health-facility-confirmed recall. Wealth quintile, maternal education, residence, and distance to primary health center were analyzed using mixed-effects logistic regression. A composite outbreak risk index was mapped at the LGA level. Results: MCV1 coverage was 64.2% (95% CI: 61.4-66.9), and full immunization was 48.5% (95% CI: 45.7-51.3). The lowest wealth quintile had 3.42 times higher odds of nonvaccination than the highest (aOR = 3.42; 95% CI: 2.41-4.86). Maternal lack of formal education (adjusted odds ratio [aOR] = 2.89; 95% CI: 2.03-4.12) and rural residence (aOR = 1.94; 95% CI: 1.46-2.58) were independent predictors. The Erreygers concentration index showed a prorich inequality of +0.324. High outbreak risk was clustered in the riverine LGAs, Port Harcourt, and Obio-Akpor slums. Conclusion: Measles coverage in Rivers State is far below elimination targets, with marked socioeconomic and geographic disparities. Targeted interventions for the poorest households, less educated mothers, and remote LGAs are urgently needed to reduce outbreak risk.