Addressing extreme heat has emerged as a key frontier of urban climateadaptation planning. However, most studies have focused on large cities,whereas most of the existing urban population lives and urban growthoccurs in small- to medium-sized municipalities within metropolitanareas in the U.S. and globally. We hypothesise based on structurationtheory that these smaller municipalities face fundamentally differentconstraints and opportunities to enhance their heat planningcapabilities than large cities. Accordingly, in this study we analyze heatplanning capacity, current activities, and expansion opportunities insmall- to medium-sized cities across two neighbouring but distinctregions in California: northern Los Angeles County (n = 20) and thesouthern San Joaquin Valley (n = 38). Using data from these 58 cities,we first comprehensively reviewed heat-related activities in their keyplanning documents. We then conducted 17 semi-structured interviewswith local government planners, planning consultants, and utilities’ staffto more holistically analyze how heat planning and implementationoccurs on the ground. The planning document analysis shows that anarrow majority of cities identified heat as a general issue of concern.The most common long-term adaptation and resilience strategies wereenhancing urban tree canopy, green infrastructure, and shadestructures, but both prevalence and strategy type vary by heatexposure level, population size, and the socioeconomic status of cities.However, in interviews, we generally found that while local officials hadhigh levels of heat awareness, they had low levels of focused capacityand deployed heat interventions compared with other climateadaptation efforts.