Under the framework of new-type urbanization and balanced regional development, counties have become pivotal spatial units linking urban expansion with socio-economic transformation. As fundamental carriers of population redistribution and industrial restructuring, county-level territories play a critical role in shaping China’s evolving urban system. However, existing studies primarily focus on prefectural or metropolitan scales and often rely on global or single-scale models, thereby overlooking spatial heterogeneity and scale-dependent effects in urbanization processes. Using county-level data for 2010 and 2020, this study investigates the spatial patterns and temporal dynamics of urbanization rates across China and explores their multi-scale driving mechanisms. First, spatial autocorrelation and distribution characteristics are examined to identify clustering and gradient structures. Subsequently, a Multi-Scale Geographically Weighted Regression (MGWR) model is employed to disentangle the scale-specific effects of natural conditions, economic development, infrastructure provision, demographic structure, and institutional factors. The results reveal that (1) China’s county-level urbanization rate increased significantly between 2010 and 2020, exhibiting a persistent east–west gradient and pronounced coastal agglomeration; (2) economic development and transportation accessibility are dominant drivers nationwide, while institutional and policy-related factors demonstrate stronger localized effects in central and western regions; and (3) different explanatory variables operate at distinct spatial scales, highlighting substantial spatial heterogeneity in the mechanisms underlying urbanization. This study contributes to a more nuanced understanding of county-level urbanization within the broader urbanization and social development process and provides empirical evidence for differentiated and place-based urbanization policies aimed at promoting coordinated regional development.