In May 2003 the University of Wisconsin Applied Population Laboratory initiated a comparison of the pooled 1999 – 2001 American Community Survey (ACS) data with the corresponding Census 2000 long form population and housing characteristics for the county and census tract levels in Oneida and Vilas Counties (Wisconsin) and Lake and Flathead Counties (Montana) on behalf of the U.S. Census Bureau. This document presents the key findings of this analysis.