To combat biodiversity loss in the United States, imperiled species are protected under the federal Endangered Species Act (ESA), which is currently threatened by political initiatives seeking to weaken it and potentially transfer substantial authority to the states. To assess the conservation capacity of current state laws, we conducted a quantitative analysis of imperiled species protection within all 50 states by compiling data on all state-listed species, ESA-listed species, and IUCN Red List species in each state.We found that currently 16% of ESA-listed species and 52% of IUCN imperiled species are not protected by any state law, and if the ESA were repealed these numbers could increase to 73% of ESA-listed species and 81% of IUCN imperiled species unprotected. Although protection varies widely among states, our results suggest that revoking the ESA would be highly detrimental to imperiled species conservation and recovery in the United States.