From a Pew Internet article:

56% of all Americans have accessed the internet by wireless means.

An April 2009 survey conducted by the Pew Research Center’s Internet & American Life Project asked respondents whether they had used a variety of devices – laptops, cell phones, game consoles, and more – to go online using a wireless network. Altogether, 56% of Americans said they have at some point used wireless means for online access.

Read the rest of the article here.