IFLA (International Federation of Library Associations and Institutions) Library Map of the World is a representative source of basic library statistics and a robust tool providing country-level data and a worldwide comparison of different library performance metrics by region.
Numbers for Academic Libraries come from the National Center for Education Statistics Academic Libraries: 2012 First Look survey
The Public Libraries Survey (PLS) provides statistics on the status of public libraries in the United States.
The data are collected from approximately 9,000 public libraries with approximately 17,000 individual public library outlets (main libraries, branches, and bookmobiles) in the 50 states, the District of Columbia, and outlying territories.
Data includes information about library visits, circulation, size of collections, public service hours, staffing, electronic resources, operating revenues and expenditures and number of service outlets.
Numbers for Public School and Private School Libraries come from the NCES Characteristics of Public and Private Elementary and Secondary Schools in the United States: Results From the 2011–12 Schools and Staffing Survey
Reports of findings from the 2011-12 survey for 116,240 K-12 schools in the U.S. covering numbers of schools, staffing, graduation rates, and other school-wide characteristics.
Numbers for Bureau of Indian Education School Libraries come from Characteristics of Public and Bureau of Indian Education Elementary and Secondary School Library Media Centers in the United States: Results from the 2007-08 Schools and Staffing Survey