This paper studies how local supplier agglomeration is related to buyer-supplier reconfiguration in production networks, with evidence from China’s automotive industry. Using detailed panel data constructed from multiple MarkLines datasets for 2011 to 2024, I study whether firms located in denser local supplier environments are more likely to switch suppliers and, conditional on switching, whether they choose geographically closer replacement suppliers. The analysis combines product-level buyer-supplier links with plant-level production information, allowing the construction of a plant by product by year panel with geographic distance measures between buyers and suppliers. I document three main empirical patterns using the merged dataset. First of all, firms in denser supplier environments exhibit higher rates of supplier switching. Second, among switching events, firms in denser local markets tend to choose geographically closer replacement suppliers. Third, switching in denser supplier environments is associated with larger inward adjustments in buyer-supplier distance relative to the incumbent relationship. These findings suggest that thicker local supplier markets are associated with both more frequent and more localized reconfiguration of production networks. In addition, I examine heterogeneity across product categories by incorporating category-level measures of standardization, value density, and distance sensitivity, and show that the effects of supplier agglomeration are stronger in categories where geographic frictions are more important. To interpret the economic forces behind these patterns, I develop a simple conceptual framework in which buyers face search frictions and consider only a subset of potential suppliers. Agglomeration expands this consideration set, especially for nearby suppliers, thereby increasing the likelihood of switching and making local replacement more likely. The paper provides empirical facts that may inform future work on dynamic production network adjustment.