Hazard mitigation plans can support communities’ resilience in the context of natural hazards and climate change. The quality of these plans can be evaluated using established indicators; however, research is also needed regarding the perceptions of participants in planning processes, to understand aspects of the planning processes that may not be evident in the plan documents. This study builds on previously reported plan quality scores and survey data, to investigate whether selected collaboration dynamics (principled engagement and capacity for joint action) occurred during counties’ hazard planning processes. Semi-structured interviews were conducted with 20 hazard planning professionals who were involved in preparing county-level hazard mitigation plans in Washington State, USA. Findings (for cases with both high- and low-scoring plans) include evidence of collaboration dynamics, although important participants (e.g., members of the local community) were reportedly missing from some planning processes, raising concerns about the extent to which the plans reflect local needs. These results are consistent with previous literature, which has demonstrated that members of the public often view hazard mitigation as inaccessible and disconnected from their daily lives. The paper concludes with recommendations for how practitioners might go about bolstering participation from important participants, potentially leading to higher-quality plans and helping to protect communities from hazards.