The ACS collects data in three phases: mailout/mailback, telephone interview, and Computer Assisted Personal Interview (CAPI). During the CAPI phase, a sample of mail/telephone non-respondents and addresses deemed to be unmailable is selected for a personal visit. Th e sampling rate for this process is determined by the CAPI sampling stratum for the tract in which the address resides, which is assigned based upon the mail/telephone cooperation rate of the tract. Th e initial assignment was made prior to 2005. Based upon recent ACS data, cooperation rates were re-calculated for all tracts, which were then assigned to a new CAPI sampling stratum. Th is paper discusses the data that led us to revisit the CAPI sampling stratum assignments, and it provides the methodology used to calculate the tract level mail/telephone cooperation rates used to assign each area to a CAPI sampling stratum.