Urbanization reshapes ecosystems by fragmenting habitats, limiting gene flow, and altering host–pathogen interactions, which can drive immune gene evolution. We are investigating how urbanization affects immunogenetic diversity in house finches (Haemorhous mexicanus) by analyzing four Toll-like receptor loci (TLR2B, TLR3, TLR4, and TLR15). Finches were sampled from urban, suburban, and rural sites in Fresno and Madera Counties, California, to test whether allele frequencies, genetic diversity, and selection patterns differ at these loci at each urbanization level. We extracted DNA, performed PCR for most loci, and sequence analysis is underway. We predict that urban populations will show reduced TLR diversity due to restricted dispersal and environmental uniformity, while suburban and rural populations retain higher variation. However, we also expect evidence of diversifying selection, indicating that pathogens continue to shape immune gene evolution in all environments. By comparing immune gene variation based on urbanization intensity, we aim to determine whether selection maintains functional diversity despite limited gene flow. This research links molecular evolution to human-driven environmental change and advances understanding of how wildlife populations adapt to urbanization.