This research project was about the assessment of the effectiveness of monitoring and evaluation system in the implementation of County government projects. Effective monitoring and evaluation implies the ability of the M & E system to aid in the successful implementation of a project by achieving its objectives. The study was based on four objectives; one, to assess how monitoring and evaluation planning influences the implementation of projects in Kirinyaga County Government, two to examine how funding for M & E influences implementation of projects in Kirinyaga County Government, three, to determine how technical expertise for M & E influences implementation of projects in Kirinyaga County Government and lastly to establish how stakeholders' participation in M & E influences implementation of projects in Kirinyaga County Government. As much as standards dictates that projects must be monitored for proper control, there is also need for stakeholders to get the accountability for their resources used in the project, performance of project and also benefit of the project implemented. Therefore, the researcher undertook an in depth review of the existing literature on the variables of interest. From the existing literature it's evident that participatory planning for monitoring and evaluation at the onset of a project is key to the implementation of projects as it allows incorporation of all the elements of monitoring and evaluation, the indicators and the funding needs as well as the persons responsible for the M & E activities. To actualize the plan, reviewed literatures indicate need of proper funding and technical expertise of the staff and the people involved. Previous also indicate the importance of stakeholders' participation in giving divergent viewpoints but affirms that stakeholders should not be allowed to have greater control and that the management should remain in charge. The study was undertaken in Kirinyaga County and adopted a descriptive survey design with questionnaire as the main data collection tool and the target population drawn from the county government employees. The researcher employed a stratified random sampling to draw the sample. From the data analyzed, it was evident that all the four variables of M&E planning, M&E funding, M&E Technical expertise and Stakeholder participation had influence on the implementation of project at the County Government of Kirinyaga with a Pearson correlation coefficient of 0.601, 0.600, 0.644 and 0.676 respectively, an indication of a moderately strong correlation. The researcher also summarized the findings, drew conclusions and given recommendations that County government should ensure all projects have M & E plan prepared at the onset of the project through a participatory process; the county government should ensure adequacy and proper management of M & E fund; expansion of the technical expertise of the M & E knowledge base in the county through workshops and seminar trainings and lastly to ensure controlled participation of stakeholders by putting up a system for identifying and managing stakeholders where only key stakeholders should be allowed to take part in M & E.The study was intended to inform both the county and national government of how effective monitoring and evaluations is vital in the implementation of projects undertaken by the County Governments and the importance of the M & E data in strategic planning for the county development projects.