The rumen microbiome has a direct impact on animal health and performance and as such is an important metric for the comparison of cows across regions and diets. The impact of geography, farm management, and other environmental factors on the rumen microbiome of dairy cows remains uncharacterized to date. The objective of this study was to survey the microbial composition of dairy cows across a range of farms in diverse geographies of Argentina and relate the taxonomic compositions and diversity metrics to farm-specific factors such as diet and feed management regimen. In total, 299 samples from 198 dairy cows across 10 farms in Argentina were sampled to identify trends and factors that influence rumen microbial composition. Bacterial and fungal populations were characterized via 16S rRNA and ITS gene amplicon sequencing, respectively, of rumen and fecal samples. Sequences were processed using the USEARCH pipeline and classified against the RDP database. High level trends identified a core rumen microbiome composed of 795 OTUs shared across all farms. However, distinct microbial compositions and unique taxa were also identified for each farm, resulting in strong clustering of β diversity by farm as determined by principal coordinate analysis with and without the core microbiome included. The forage content of the diet was also shown to have an important role in defining the microbiome of the host animal. Taken together, these findings represent a key step toward identifying the link between environmental factors and farm management on the rumen microbiome.