Following implementation of a devolved county government in Kenya in 2010 which followed devolving huge resources, adoption of Integrated Financial Management Information Systems (IFMIS) has been seen instrumental towards effective county management practices. These devolved resources need to be managed prudently for the citizens to enjoy the fruits of devolution. This study sought to assess the contribution of IFMIS on the effectiveness of management practices of Nairobi and Lamu Counties. The specific objective of the study was to; determine the influence of budgeting process automation on effective management practices; to establish the influence of automated county services on effective management practices; to establish whether computerized human resource management has increased effective management practices; and to establish the influence of automated procurement and disposal processes on effective management practices in Nairobi as the biggest County and Lamu being the smallest county. To achieve these objectives, a correlational research design was used with the study population being employees in the county mandated and tasked with the implementation of IFMIS. Primary data was collected and analyzed using SPSS to generate descriptive and inferential statistics to describe the study results. The findings in this study revealed that IFMIS contributes significantly to the effectiveness of county management practices with p<0.05 in human resource management (51.6%), service delivery (49.4%), budgeting process (38.7%) and procurement (18%). The study concluded that IFMIS id an important too for effective county management practices and recommended areas for further research among them; establish a model for testing and evaluating the level of success in the implementation of IFMIS and to establish the role of end users on the level of success in the implementation of IFMIS in the County Governments.