A synthetic residential baseline population for the United States at the census block group level based on the American Community Survey 2015-2019 5-Year Estimates and described by residential, demographic, social, economic, student, mobility, and housing characteristics. Files are organized by state and compressed as tarballs. Each state contains a series of Apache Parquet files, one per county, containing the synthetic population records. Also included are a data dictionary and a `constraints.json` that specifies the constraining variables used for population synthesis.