Line graphs Source: Institute of Museum and Library Services, Public Libraries in the United States Survey (1990, 1995, 2000, 2006, 2011)
Why the drop in the number of libraries?
The IMLS explains in the introduction to the 2010 Public Libraries in the United States Survey.
In order to be included, a public library must meet this 5-point definition.
An example. The Central Falls (Rhode Island) Public Library closed in July 2011 and reopened 2 months later with a staff of volunteers, i.e., with no paid staff (#2) and, it appears, based on the reference to donations, no public funds (#5).