NFL attendance, by team and by year, from popular sources, Quirk and Fort, Pay Dirt, 1992, and Nola Agha at sportseconomics.com. Most historians agree that the NFL began as the American Professional Fotball Association, organized in 1920, reorganizing to the National Football League in 1922. All other leagues can be found in NFL Rival Leagues. The files are all in MSExcel format. So, use your "Save Target As" command to save them to your hard disk.
All Teams All Years (1922-24 average per game): 1922-24, 1934-1991, 1993-1997, 1999-2007