The Census Bureau's publicity campaigns assume that cooperation with the census depends on knowledge of how census data are used in the aggregate e.g., legislative apportionment and revenue sharing) and that they are not used at the individual level (i.e., identifying information is kept confidential by law). This article compares knowledge about these matters with feelings about the census as correlates of willingness to cooperate with a new census request — disclosing one's Social Security number to facilitate data sharing (a proposed way of stemming the census's skyrocketing costs and declining coverage).