Impact of county-to-district conversion on the urban-rural integration development: A case study from Jiangsu Province, China

County-to-district conversion (CDC) has restructured the pattern of urban-rural development and influenced the allocation of resources by local governments as well as the urbanization process. However, the impact and mechanism of the CDC on China’s urban-rural integration development (URID) are not yet clear. Using panel data from 52 county-level cities, districts, and counties in Jiangsu Province of China during 2005–2021, this paper constructed an evaluation system for URID and applied the multi-period difference-in-differences (DID) model to measure the impact of the CDC on URID and identify its primary mechanisms of action. The results demonstrated that the CDC has significantly fostered URID, though with pronounced regional heterogeneity. Specifically, while the CDC facilitated URID in the southern and central Jiangsu Province—regions characterized by high socio-economic development—it exerted a less significant impact in the comparatively underdeveloped northern Jiangsu Province. Mechanistically, the implementation of the CDC promotes equal regional development, enhances rural self-development capacity, improves environmental quality and living standards, and optimizes urban-rural land allocation and transport networks. Ultimately, this study clarifies the role of the CDC in China, provides insights for achieving URID, and offers a reference for other countries pursuing coordinated urban-rural development.