State and national FY90 data are aggregated from individual public libraries in the United States. These data were collected under the third annual census of the Federal-State Cooperative System (FSCS) in July of 1991. Respondents for this voluntary census were 8,978 public libraries identified in the 50 states and the District of Columbia by state library agencies. This report begins by presenting highlights of the findings. The introduction then describes the universe represented by the data, data collection and use of technology, quality review, and unit and item responses to the survey. Also included are caveats for using the data, information for ordering related machine-readable data and publications, and a source for additional information on public library statistics. (It is noted that data on individual libraries, which are not included in this report, will be available on diskette.) The data are presented in 15 pairs of tables, which make up the major part of the report. These tables summarize information that was supplied to National Center for Education Statistics (NCES) in machine-readable format by state library agencies on a voluntary basis. The information includes data on staffing, service outlets, operating income and expenditures, size of collection, and service measures such as reference transactions, interlibrary loans, circulation, and public service hours. Four appendices provide information on the background of the Federal-State Cooperative System (FSCS); data error messages and historical data check criteria; a nationwide item non-response chart; and data element specifications for 1990. (BBM)