Despite their crucial role in expanding educational opportunity across P-20 education and supporting regional wellbeing, there is no official list of RPUs. In large part due to an absence of a list of RPUs and a systematic way to identify and define them, until very recently RPUs were largely invisible in scholarly and policy discussions. As a result, sector-wide quantitative data and research are nearly nonexistent, and RPUs and their students experience invisibility in consequential policy and scholarly discussions. This study identified, defined, and examined the entire RPU sector and its students using an inductive, data-driven approach that identified RPUs that exhibited similar missions and institutional characteristics. This study also contributes a data infrastructure to support future quantitative inquiry into these vital institutions.