Tribal research review boards (TRRBs) assert the sovereign rights of tribal nations by requiring internal approval of research activity conducted within their jurisdiction. The requirements for research approval are often poorly understood by researchers. In this study, we locate and characterize the information available for TRRBs in the U.S. through a systematic examination of federal registrations, online presence and documentation, and information requests. Expanding on a previous study, we enumerate active TRRBs with an online presence and discuss the types of documentation required by each entity. Our results support ethical research practices by researchers and tribal communities as they expand their understanding of TRRBs.