The 2010 Census and the American Community Survey (ACS) both measure occupancy status, vacancy status, and household size. This report will: (1) document comparisons of published information on these measures from the 2010 ACS with the 2010 Census (2) discuss the design and methodology differences of the ACS and the 2010 Census that likely contribute to the observed measurement differences We will highlight where differences exist and identify possible explanations for the differences. These differences do not necessarily imply errors exist in either the ACS or the 2010 Census results. To the extent interviewers and enumerators misclassified housing units, this report will not try to determine if the ACS or the Census was more correct.