Mule deer (Odocoileus hemionus) populations in southern Oregon have experienced significant declines, particularly in the Klamath Basin, where reduced fawn survival is a management concern. Factors affecting population decline such as habitat change, climate variability, and predation have been widely studied, but the role of parasitism in influencing herd health and recruitment remains less well understood. This thesis examined patterns of gastrointestinal parasitism through descriptive and comparative analyses aimed at better understanding the parasite prevalence, and parasite load in mule deer across two mule deer herd ranges with declining populations. Fecal samples collected from mule deer across Klamath County were analyzed using fecal floatation and centrifugation techniques to identify gastrointestinal parasite ova and estimate parasite burden. Preliminary descriptive sampling documented variations in parasite prevalence, parasite load, and parasite species richness within the study area. A more structured comparative analysis was then conducted to compare parasite prevalence and parasite load trends between the Klamath and Keno herd ranges. Fecal samples (n=91) were classified by infection status and parasite load, and binomial generalized linear models were used to test for herd level differences in infection probability and high parasite burden. Parasite prevalence differed significantly between herd ranges, with deer sampled from the Klamath herd range exhibiting substantially higher probability of infection. Parasite load across all sampled individuals was also greater in Klamath, however parasite load among infected individuals did not differ significantly, indicating that the observed differences were primarily caused by greater prevalence in Klamath rather than host-level susceptibility to parasitic infection. Collectively, these findings show that gastrointestinal parasitism is widespread in southern Oregon’s mule deer, and that the burden of parasitism is not homogenous among populations. The elevated prevalence observed in the Klamath Basin herd range suggests that parasitism may be interacting with other population limiting factors to influence fawn survival and herd health, while highlighting parasitism as an ecological factor warranting further investigation in these populations.