Since 2000, the Autism and Developmental Disabilities Network (ADDM) has published detailed prevalence estimates for autism spectrum disorder (ASD) among 8 year-olds, which are widely interpreted as the U.S. national prevalence of ASD. Although differences in state-level ASD prevalence has been reported, state-level heterogeneity has not been explored systematically. We analyzed state-level estimates and trends in ASD prevalence from 2000 to 2012 using secondary data from bi-annual ADDM reports. Heterogeneity among state-level ASD prevalence estimates were apparent in 2000 and grew between 2000 and 2012. Findings highlight the need for greater understanding of how children with ASD are identified by the medical and educational systems, which has significant implications for the state-level resources required to effectively manage ASD.