Neighborhood environments are increasingly thought to affect emergency department (ED) use. However, because people decide where to live based on a range of factors, it can be challenging to identify the causal impact of living in higher-poverty neighborhoods on increased rates of ED visits. Our study leveraged the Moving to Opportunity for Fair Housing Demonstration Program, a social experiment beginning in 1994 that randomly assigned approximately 4,600 households that received federal housing assistance to different neighborhood conditions. We linked program participants in four states with an average of twelve years of administrative data on ED use (up to twenty-one years after randomization). Contrary to our expectations, we did not find a consistently significant connection between neighborhood poverty and overall ED use during this follow-up period. This result was observed for both adults and people who were children at the time of randomization, as well as for various classifications of ED visits. The findings can help direct future research that seeks to clarify the relationship between neighborhood environments and health care use.