IMLS recently published the 2008 Public Libraries Survey Report: https://www.imls.gov/sites/default/files/publications/documents/pls2008_0.pdf.
An analysis of the data shows that nationally public library visits and circulation went up 20% from 1999 to 2000 while staff numbers stay the same: https://www.imls.gov/news/public-library-visits-circulation-spike-while-staff-numbers-stay-same-imls-fy2008-public