Financial management in county governments plays a crucial role in promoting good governance. The national government allocates county governments more than stipulated 15% of national revenue yearly yet 53.0% of them are classified as very poor, 36.1% fall below the national poverty rate and that 34% fall below the national hardcore poverty line. The general objective for this study was to determine the relationship between internal control practices and service delivery of County Governments in Nairobi Metropolitan Area, Kenya. Agency theory and optimal tax theory served as the foundational frameworks for this research. These theories guided the formulation of conceptual framework, informed the study design and methodology, and aided in the interpretation of findings. A cross sectional correlation research design grounded in the philosophy of positivism was employed in this study. Primary data was collected using structured questionnaire. The study’s target population was 163 directors from Counties in Nairobi Metropolitan Area, Kenya. Purposive sampling approach was employed to get a sample of 116 respondents. The data was analyzed using descriptive and inferential statistics. Descriptive statistics was used to describe the data while correlation, regression and moderated regression analyses were used to address the objectives of the study. The study found that internal controls practices demonstrated a significant positive relationship with service delivery, with a correlation coefficient (r) of 0.607, a beta coefficient (β) of 0.776 (p<0.05). The study concludes that effective internal controls practices is crucial for enhancing service delivery in the County Governments of the Nairobi Metropolitan Area. This study recommends that, to ensure service delivery, public institutions should focus on internal control practices. This study makes important contribution to the government and to the scholars.