Mammals have played a foundational role in the explosive growth of phylogeography over the past 30 years that it has been a recognized discipline. Novel discoveries of geographic patterns and processes using phylogeographic approaches have integrated disciplines including biogeography, evolutionary biology, ecology, and conservation biology. Here, we use several approaches to survey the scope and influence of phylogeography, beginning with use of a well-studied family of North American rodents to contrast information content derived from DNA-based phylogeography versus a popular older method, allozyme electrophoresis, of assaying genetic variation within and among species across geography. We conclude that phylogeography has elevated the quality of insights attainable regarding, for example, the causal role of Earth history events in processes including lineage divergence, speciation, and adaptive evolution. Next, we use searches of the Web of Science with an array of terms that return information on molecular markers employed, numbers of individuals and localities examined, time frames investigated, historical processes and ways that species and biotas have responded to Earth history, design of phylogeographic studies (e.g., single-taxon versus comparative), and current gaps in taxonomic and geographic sampling. Highlighted results from phylogeographic assays include: an average of 3.3 cryptic lineages per taxonomic species in rodents; a bias in number of studies toward less-diverse biogeographic regions; and a relatively low number of mammalian genera studied. We conclude with predicted and recommended directions for future growth in mammalian phylogeography, including prospects for an increasing role of next generation-based genomics.