Agriculture is the main stay and driver of Kenyan rural economy. Despites the critical role of agriculture in Kenya, poor access to extension support services still persist. This study sought to determine the factors influencing delivery of extension services by the county governments after agricultural sector devolution as per the Constitution of Kenya (2010). The study used an ex post facto descriptive survey design. A total sample of 70 extension officers drawn from the population of 241 extension officers were selected from Kitui County using a stratified random sampling approach. Secondary sources of information such as county reports and existing literature were examined to complement the primary survey data. Questionnaires were administered to the sampled extension officers. Data analysis was carried out using descriptive, inferential statistics and linear regression. This study found that majority of extension officers reported inadequate performance in extension service delivery by the county government due to factors such as unavailability of transport, delayed salaries, lack of staff promotion, undefined duties with duplication, unfavorable and poor work environment and low facilitation for extension activities. This study recommends that for better extension service delivery in Kitui County, extension officers should be well facilitated through mode of transport, proper remuneration and timely promotions. Greater support and budget should be directed to the devolved agricultural extension services as a way of improving agricultural productivity and increasing farmers’ incomes.