Recent estimates reaffirm that conservation funds are insufficient to meet biodiversity conservation goals. Organisations focused on biodiversity conservation therefore need to capitalise on investments that societies make in environmental protection that provide ancillary benefits to biodiversity. Here, we undertake the first assessment of the potential ancillary benefits from the ballot box in the United States, where citizens vote on referenda to conserve lands for reasons that may not include biodiversity directly but that indirectly might enhance biodiversity conservation. Our results suggest that referenda occur in counties with significantly greater biodiversity than counties chosen at random. We also demonstrate that large potential gains for conservation are possible if the past and likely future outcomes of these ballot box measures are directly incorporated into national-scale conservation planning efforts. The possible synergies between ballot box measures and other biodiversity conservation efforts offer an under-utilised resource for supporting conservation.