Performance in the Police Service in Kenya has been deteriorating over the years. For this reason, the National Police Service has recently developed an ambitious plan for police reforms, aimed at transforming the Police Service into an institution that will be modern, efficient and effective and responsive to the needs and expectations of the public. However, there seems to be a problem in the police reform program. Accordingly, the present study sought to ascertain the effectiveness of police service reforms on service delivery in the Kenya Police Service in Nairobi County, Kenya. Its objectives are to establish the effectiveness of personnel reforms on service delivery in the Kenya Police Service in Nairobi County; to establish the effectiveness of financial reforms on service delivery in Kenya Police Service in Nairobi County; to establish the effectiveness of legal reforms on service delivery in Kenya Police Service in Nairobi County; and to establish the effectiveness of cultural reforms on service delivery in Kenya Police Service in Nairobi County; The study adopted a descriptive, survey design and was cross-sectional in nature. The study was delimited to Nairobi County, Kenya and the respondents comprised of junior cadre police officers who are the main operatives on patrols and front office desks. A sample of 351 respondents was selected from a target population of 2883 officers using stratified random sampling. Primary data was collected using a questionnaire while secondary data was collected through a review of relevant content. Out of the 351 questionnaires that were distributed to the targeted respondents, one hundred and two were correctly filled and returned. Data was analyzed by use of descriptive statistics and presented using a pie chart, tables and narration. The results reveal that police service reforms are broadly