The Internet Archive curated a 90-terabyte sub-collection of captures from the US government's public website domain (‘.gov’). Such archives provide largely untapped resources for measuring attributes, behaviors and outcomes relevant to political science research. This study leverages this archive to measure a novel dimension of federal legislators' religiosity: their proportional use of religious rhetoric on official congressional websites (2006–2012). This scalable, time-variant measure improves upon more costly, time-invariant conventional approaches to measuring legislator attributes. The authors demonstrate the validity of this method for measuring legislators' public-facing religiosity and discuss the contributions and limitations of using archived Internet data for scientific analysis. This research makes three applied methodological contributions: (1) it develops a new measure for legislator religiosity, (2) it models an improved, more comprehensive approach to analyzing congressional communications and (3) it demonstrates the unprecedented potential that archived Internet data offer to researchers seeking to develop meaningful, cost-effective approaches to analyzing political phenomena.