In the United States, selected subgroups of historically marginalized populations include people with disabilities and people in racial/ethnic minority groups ("critical populations") who have been disproportionately affected by COVID-19. These groups are also more likely to use public transit to access essential resources; thus, understanding transit agencies' communication strategies to reach these populations during crises is of utmost importance. We conducted a content analysis of 16 transit agencies' webpages and Twitter® accounts during the first 6 months of the pandemic to assess alignment of agencies' COVID-19-related communications with best practices in crisis communication across five themes: perceivability, navigability, understandability, suitability, and content. Findings suggested that transit agencies frequently communicated about schedule changes and safety, eg, masking, station sanitation, and reflected racial/ethnic diversity in images. Yet, less than half consistently used communication strategies known to enhance accessibility and uptake of messaging among critical populations, eg, alternative text, and even less reflected disability diversity in images. We offer recommendations for public transit agencies to move beyond compliance to effectively address the needs of ridership most substantially impacted by public health emergencies.