Abstract: The integration of the Yangtze River Delta region and shifts in population concentration and movement have spurred a transformation in the traditional patterns of county-level development in Jiangsu Province. And it has led to a more intricate and multifaceted trajectory of differentiation. This article retraces the 'three iterations' of county-level development in Jiangsu Province and presents the logical threads of the dynamic alignment between industrial function and population mobility across different stages. On this foundation, the article exposes the emergence of two novel phenomena: the 'regrowth of advantageous areas' and the 'reverse growth amidst contraction'. These revelations stem from an analysis grounded in population change data in Jiangsu Province. Furthermore, the article identifies distinct mechanisms: 'integrating into a metropolitan area' 'integrating into a regional network' 'adjusting contraction' and 'perforating counter-growth'. Ultimately, drawing on the practical experiences of these mechanisms, the article offers recommendations for aligning growth and contraction strategies from the angles of industrial development guidance, land resource allocation, and fiscal policy formulation.