Once every 10 years, the National Archives and Records Administration (NARA) makes millions of U.S. census records available for use by eager historians and genealogists. The release of a new batch of census records is a highly anticipated event, but only for the select few who are able to access the published microfilm versions of the census. That changed on April 2, 2012, when NARA published the 1940 census online, making it available instantly and free of charge. The 1940 census includes a remarkable collection of information. Census enumerators collected information on 81 topics. Given that the census is perhaps the single most important collection of American historical records, the online publication of the 1940 census was an immediate sensation. The release of the 1940 census offers social studies teachers and students valuable opportunities to learn about history. By using the census records, teachers can open a window into the past for their students, and introduce to them a remarkable assortment of scholars and enthusiasts doing history. In this article, the authors describe how the historical records in the census are suited for a wide range of historical analysis, including mining for quantitative data that show patterns of life in the United States, constructing narratives of places and people around the country, and enabling a type of personal and biographical search that is appealing to students (using the example of Thaddeus Lee). The article concludes with implications for classroom teachers, steps for getting started, and recommended inquiry-based activities using the digitized 1940 census.