Using detailed household data, we find that households working in locally agglomerated economies have high mortgage loans and are more likely to have mortgage loans. Channel testing shows that local agglomeration increases housing and mortgage demand as well as mortgage supply. The increase in mortgage loans is driven by purchases of larger houses and smaller down payments. Mechanism analyses document that local agglomeration affects mortgage loans by increasing career upward potential and providing downside protection. Specifically, we find that the impact of local agglomeration is stronger for skilled employees with enhanced prospects. In addition, local agglomeration weakens the negative relation between unemployment and mortgage loans, which supports the downside-protection role of local agglomeration. These results hold under instrumental variables analysis, difference-in-difference analysis, and a set of robustness checks. Overall, our findings highlight the importance of local labor market composition in household mortgage debt. This paper was accepted by Kay Giesecke, finance. Funding: F. F. Chen acknowledges the financial support provided by the Fundamental Research Funds for the Central Universities; the MOE Project of Key Research Institute of Humanities and Social Science in University [Grant 22JJD790094]; and the 111 Project [Grant B18033]. Supplemental Material: The data files are available at https://doi.org/10.1287/mnsc.2022.03486 .