The Great Lakes Cosmology Workshop is a forum for students, postdocs, and senior scientists from around the Great Lakes region, North America, and the world to meet and discuss the latest results, ideas, and problems in modern cosmology. The 2020s will be the decade of large surveys of the spatial, spectral, and temporal characteristics of the cosmos, and current and upcoming instruments, measurements, and scientific interpretations promise to transform our understanding of the history and origin of cosmic structure. The 12th Great Lakes Cosmology Workshop will be held in Rochester, NY in August 2019 and will provide an opportunity for scientists working in the field to come together in an open, inclusive workshop devoted to understanding the origin, state, and fate of our universe and the structures within it.