While all sites in the Top 10 saw an increase in unique U.S. visitors during the month, Amazon had the largest increase (5.9%) among the top sites.  Visitors to Facebook’s website spent the most time on average, logging over 7 hours 45 minutes using the social network over the course of the month. AOL also increased the amount of time spent by average visitors on their site by over 25% during August.

Overall 215 million Americans were active on the Internet in August 2011, an increase of 1.2% compared to the previous month. On average Americans spent over 30 hours online during August and visited 99 unique domains. Nielsen estimates 275 million Americans had access to the Internet during August 2011.

* – Due to a change in the type of call used behind Facebook’s AJAX interface, Nielsen NetView data for Facebook duration was underreported for June and July, impacting overall web use figures for those months. Therefore, Time Spent and Page Views per Person for August should not be trended against July 2011 data.

With 13.2 million unique U.S. visitors in January 2011, the Huffington Post was the ninth most popular non-financial news website visited from home and work computers in the U.S. Its new ‘sister’ site, AOL News, was the fourth most-popular with 22.1 million U.S.-based unique visitors. AOL News is AOL’s second most popular channel – behind MapQuest – and, in effect, the Huffington Post becomes AOL’s sixth most popular property just behind AOL Messenger/AIM (with 13.3 million uniques in January) and ahead of AOL Music (with 13.1 million).

AOL’s network of websites attracted 76.2 million unique U.S. visitors in January 2011, or 39 percent of all active U.S. web users. Visitors to AOL’s websites spent an average of 1 hour 58 minutes during the month, viewing 85 pages on average. Based on average visitor January figures, each Huffington Post reader adds almost 12 minutes of time and 18 pages to the AOL portfolio – a total of 155 million minutes and 237 million page views.

Although the Huffington Post had 13.2 million U.S. uniques in January, almost 10.2 million of them also visited an AOL website, thus the net effect of AOL’s acquisition is almost 3.1 million new visitors or 1.5 percent more reach into the active U.S. Internet population. There is also a strong overlap between the Huffington Post and AOL News. In January 2011, 44 percent of visitors to the Huffington Post also visited AOL News; with 27 percent of AOL News readers also visiting the Huffington Post.

It’s not just about the extra readers the acquisition brings but the type of visitor. Although the audience makeup to AOL News and the Huffington Post is broadly similar, the latter is more concentrated around certain demographic groups. For example, the Huffington Post has a higher concentration (34%) of 18-49 year old females compared to 29 pecent for AOL News. The Internet average is 27 percent.

Although the audiences to the two entities are spread similarly geographically across the U.S., it is notable that the Huffington Post is more likely to have visitors from the West Coast while AOL News tends to have a greater concentration of visitors from New England.

The Huffington Post audience also tends to be more highly-educated – 44 percent hold a bachelor or post-graduate degree, compared to 37 percent for AOL News, 31 percent across the entire AOL portfolio and 25 percent across the entire web.

A very encouraging element of Huffington Post reader behavior for AOL concerns who consumes content. Visitors from households with incomes above $150,000 account for twice the percentage of total page views consumed on Huffington Post (12%) than they account for on AOL News (7%) and across the entire Internet (6%).

Those with a bachelor’s degree account for 50 percent more of Huffington Post content (33%) compared to AOL News (24%) and the Internet average (22%). Most starkly, those with a post-grad degree account for almost three times the percentage of Huffington Post content (34%) than they average across the whole Internet and AOL News (both 12%).

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View the top U.S. Web brands for September and October 2008.

Yahoo! and MSN/Windows Live rounded out the top three, with unique audiences of just over 116 million and 102 million visitors, respectively.

View the full press release.

View the top U.S. Web brands for September 2008.