Abstract: In-situ urbanization with county towns as key carriers represents a critical pathway for promoting integrated urban-rural development and achieving rural revitalization in the new era. On the basis of defining the conceptual characteristics of in-situ urbanization with county towns as key carriers, this study measures the level of in-situ urbanization in county towns, analyzing its driving mechanisms through dimensions such as resource conditions, industrial economy, infrastructure development, and investment-driven forces. Based on empirical analysis of Jiangsu and Sichuan provinces, five models of in-situ urbanization in the two provinces are summarized into five categories: the metropolitan-periphery model, the regional node model, the resource-driven model, the major agricultural production area model, and the policy-led model. To support pragmatic zoning, classification, and targeted policy implementation, differentiated policy measures are implemented across three dimensions: population migration guidance, fiscal transfer payments, and governance of main functional zones.