The level of preparedness of the counties to face the challenges of effective service delivery of the devolved functions and potential complexities to ensure that they are managed strategically is a major concern. Devolution faces myriad challenges thereby falling short of addressing implementation of devolved functions. This study endeavored to investigate the determinants of implementation of devolved functions in Machakos County. The specific objectives of the study are to: evaluate whether training determines implementation of devolved functions; assess whether local resource mobilization determines implementation of devolved functions; establish whether fiscal measures determine implementation of devolved functions; and to evaluate whether administrative structure determines implementation of devolved functions in Machakos County. This study was premised on four theories namely dynamic capabilities, decentralization, systems, and institutional theory as the theoretical underpinning to help realize the objectives of the study. The study adopted a descriptive case study research design that utilized both qualitative and quantitative approaches, carried out in the county government offices in Machakos County. The target population of 6108 comprising of four strata of staff in Machakos County had a sample of 301 participants selected using both purposive and stratified random sampling. Questionnaires were the main instrument of data collection, complemented with interview schedules for senior administrative staff. The quantitative data collected was edited, coded, classified on the basis of similarity and then analyzed using SPSS software version 22.0, whereas qualitative data was analyzed using NVIVO, and then categorized thematically.