[Air-l] american internet penetration stats?

Has anyone got a good source of estimates of internet penetration in the United States over time? I am fanmiliar with Hobbes Internet Timelines' charts of total hosts, but that is not specifically American, and with Pew's charts, but those have enormous gaps prior to 2000. What I am hoping for is a simple summary of what percentage of Americans used the internet in 1992, 1993, 1994, 1995, etc.