This article applies an existing five-item index for measuring source credibility in the context of environmental health-risk controversy. Survey data were gathered in five upstate New York communities facing environmental health-risk issues. Analysis of the five case studies and a combined dataset (N = 870) show that the credibility index was consistently reliable across all applications. Use of the resulting index is demonstrated through a comparison of the credibility of the New York State Department of Health (active in each case), the industries associated with each case, and the newspaper providing coverage of each case. The credibility index was used to predict risk judgments in a structural equation model. Overall, the analysis demonstrated that the credibility index performed consistently well across the five cases and illuminated important differences in each. As such, the index should be a useful addition to many environmental health and risk communication studies.