Abstract: Differentiated development at the county level is key to understanding urban-rural integration, yet existing studies often analyze counties and county-level cities together, overlooking the influence of administrative establishment. Based on the 2016—2025 CCID Top 100 Counties ranking, this paper takes counties and banners as the research group and county-level cities as the control group, constructs an analytical framework of ‘administrative establishment-region/mechanism-performance', and examines the evolutionary trends and performance differences of counties in the Top 100 through three levels: overall comparison, regional comparison, and mechanism-based comparison. The findings show that, among the Top 100 counties: 1) The number of counties exhibits a V-shaped fluctuation, with top-tier seats becoming increasingly entrenched while the remaining counties remain in a dynamic catch-up-and-surpass process, and the evolution of their regional pattern is not synchronized with that of countylevel cities. 2) The development of these counties can be categorized into five types of dynamic mechanisms, with significant performance differentiation and distinct gradients in urban-rural spillover efficiency across mechanisms. 3) Counties demonstrate smaller urban-rural income gaps, yet this advantage depends on the support of regional conditions and dynamic mechanisms. Administrative establishment provides an institutional lens for understanding performance differentiation, but its effects vary under the moderating influence of regional conditions and dynamic mechanisms. The study proposes constructing a differentiated governance system to provide reference for highquality county development and urban-rural integration.