Nielsen's July 2011 "Total Internet Audience" metric, reports that Google was the most visited website in the U.S. in July with 172 million unique US visitors.
"During July 2011, 7 of the Top 10 web brands retained the same rank, with Wikipedia and Apple switching places compared to previous months. Amazon had 70.4 million unique US visitors during the month, making their site the 10th ranked during the month," Nielsen report stated.
Nielsen said that "Overall 213 million Americans were active on the Internet in July 2011 from all sources included in hybrid measurement. Internet access through home and work PCs continued to grow to 249 million individuals in the U.S. during July 2011."