The document discusses the history and purpose of the US Census and American Community Survey (ACS). The Census has counted the US population every 10 years since 1790, while the ACS provides more detailed annual estimates between Census counts. The ACS replaced the long form Census in 2010 and samples 3 million addresses per year to estimate demographic and socioeconomic trends for areas with populations over 65,000. Users must be aware of margins of error and compare similar ACS estimates (1-year, 3-year, or 5-year) when analyzing data.