Despite national efforts under the Expanded Programme on Immunization (EPI) in Kenya, immunization coverage among children under five years in Wajir County remains low, characterized by limited vaccine uptake and high dropout rates. These challenges undermine child health and slow progress toward reducing preventable morbidity and mortality. This study examined the influence of client factors on immunization coverage among children under five years in public health facilities in Wajir County, Kenya. Anchored in the Health Belief Model and guided by the positivism research philosophy, the study adopted both descriptive and explanatory research designs. The target population comprised caregivers of children under five years attending selected public health facilities in Wajir County. A total of 160 caregivers were included, and given the manageable population size, a census approach was used to collect data from all respondents. Primary data were gathered using a structured questionnaire based on a 5-point Likert scale. The findings revealed that caregiver knowledge and socioeconomic status had significant positive effects on immunization coverage, whereas cultural beliefs had a significant negative effect. The study concludes that client factors are critical determinants of immunization uptake and recommends strengthening caregiver education, addressing socio-cultural misconceptions, and reducing economic barriers to enhance coverage.