Background: Immunization coverage in different parts of the country varies widely despite efforts to improve the services. The immunization status of children is dependent on the dynamics of vaccination uptake which is complex and involves the interplay of different associated factors. Aim: To determine the immunization coverage, status and the determinants in under 5-year-old children in Owerri municipal, Imo State. Methods: The study was a community based cross-sectional study involving 420 women and 743 under 5-year-old children. A multistage sampling technique was employed and data were collected using a pretested, semi structured interviewer administered questionnaire. Data were analysed using a computer software SPSS-IBM version 20. Results: It revealed that 63.6% and 88.9% of children less than 12 months and between 12 - 59 months respectively according to households were fully immunized. The bivariate analysis showed statistically significant associations between the immunization status of the children and place of birth delivery (p < 0.0001), maternal age (p < 0.0001), level of maternal education (p < 0.01), level of maternal knowledge (p < 0.0001), religion (p < 0.05) and ethnicity (p < 0.01). Significant predictors of being fully immunized were; maternal age 25 - 29 years old (OR = 2.1), children aged 12 - 59 months (OR = 4.6), mother having tertiary education (OR = 5.4), being a Christian Catholic (OR = 12.5), hospital births (OR = 25.2) and good level of maternal knowledge (OR = 37.7). Conclusion: Immunization coverage is relatively high but not optimal among the studied population and thus there is a need to develop strategies aimed at achieving full immunization coverage as this is critical in the reduction of childhood morbidity and mortality.