Management by Objectives (MBO) is a performance management approach where employees and managers collaborate to set individual goals aligned with broader organizational objectives. While MBO's potential benefits are recognized, its effectiveness particularly in the context of varying organizational cultures and appraisal purposes, remains unclear. The general objective of the study was to investigate the relationship between MBO and employee performance within Isiolo County Government. The study specifically examined the influence of evaluation on employees’ performance in Isiolo County. The study was grounded on image theory. The population of study was 260 employees across seven county ministries. Data was collected using a questionnaire subjected to pilot study. Quantitative data was analyzed using both descriptive and inferential statistics. The study showed that overall evaluation (with a p-value of 0.897) does not significantly contribute to employee performance within the County Government of Isiolo. Therefore, the null hypothesis for evaluation was accepted. Because the study found no significant influence of evaluation on employee performance, there is a critical need for organization to refine their evaluation systems. To gain a deeper understanding of the long-term impact of evaluation on employee performance in Kenyan county governments, longitudinal research is warranted. The study recommends need for Isiolo County Government to improve its evaluation processes. Evaluators should provide valuable input to aid in performance improvement in employees of Isiolo county government.