The U.S. Census Bureau conducted an integrated communications campaign to encourage the public to respond to the 2010 Census. Since the 2010 Census aimed to count everyone, the communications campaign had to reach a multicultural population with many race=Hispanic ethnicity groups, as well as target hard-to-count subpopulations. The communications campaign included paid advertising and promotions as well as partnerships with more than 256,000 local, regional, and national organizations to promote the 2010 Census. Our multivariate statistical analyses of survey data informed the word-of-mouth campaigns through the partnerships about barriers and motivators in the hard-to-count subpopulations. These analyses identify key characteristics correlated with the heterogeneity in attitudes within the race=Hispanic ethnicity groups. The article focuses on messages and media vehicles that are the most effective among populations that are typically targeted under partnerships. We designed specific approaches to use with the different hard-to-count groups. The results about trusted voices may be useful in other social marketing programs.