The public management of funds in Tana River County has been ineffectual and the report of the auditor general has reported massive squandering of the public resources. The poor financial accountability formed the rationale of conducting the study to assess how the county's internal control system influences financial accountability in Tana River County. The study was based on four theories, namely agency cost theory, classical management theory, stewardship theory and information systems success theory. The study employed a mixed methodology and specifically a convergent parallel mixed-methods perspective. The study adopted the descriptive research design. The targeted population for the study was 324 employees in Tana River County. A stratified sampling technique was used to get the sample size of 200 respondents. The data collection instruments comprised of questionnaires and interview guides. The results of the study indicated that monitoring systems, information and communication systems, risk management systems and internal audits explain 67.4% of the variations in financial accountability. The regression results showed that risk management system is positively and significantly related to financial accountability (β=.287 p=0.000). Moreover, it was found that internal audits and financial accountability are positively and significantly related (β=.406 p=0.000). Likewise, the study found that information and communication systems and financial accountability is positively and significantly related (β=.25 p=0.000). The study also found a positive and significant relationship between monitoring and financial accountability in Tana River County. (β=.144 p=0.000). Moreover, it was revealed there is a moderating effect of government policy and regulations on the relationship between internal control systems and financial accountability in Tana River County since the coefficient of determination (R squared) increased to 73.9%. The study recommended that counties need to develop a risk management system to spur efficiency and transparency. There should be an effective management system that could evaluate risks in advance to enables counties to maintain those risks within controlled levels. The internal auditor need to be monitored regularly to minimize the chances of presenting reports with mistakes and exaggerations. There is the need to have internal reviews of revenue targets during the financial year. Moreover, it is recommended stringent measures should be taken against the county employees found with corruption cases. Keywords: Risk management system, internal audit, information and communication systems, monitoring systems, government policy and regulations, financial accountability, Tana River County, Kenya