As of July 16, Google+ is the 42nd most-visited social networking site in the U.S. and the 638th most-visited site on the web. We suspect that Google+ is even more popular now and will gain steam when it opens to the public.

According to Hitwise, Google+ had 1.8 million total visits last week, an increase of 283% from the previous week. Google+ has grown by 821% from the week ending on July 2, the first week Google+ was made available.

56% of Google+'s upstream traffic came from other Google properties last week, with 34% of that traffic coming from Google.com. And 37% of its upstream traffic came from search engines, while 21% of its traffic was driven by email.

Google+ may not be as much of a sausagefest as some early estimates claimed. According to Hitwise, 57% of visits to Google+ were from males for the four weeks ending on July 16. That doesn't mean that 57% of its users are male, but it's a sign that previous estimates were off the mark.

Google+ is dominated by young adults. Its biggest age group for the four weeks ending July 14 was the 25-34 age bracket, which accounted for 38.37% of all visits. The week before, the entire 18-34 age bracket made up just 38.11% of total visitors.

Los Angeles, New York City and San Francisco are the most dominant metropolitan areas driving traffic to Google+. Other areas with a higher proportion of visitors to Google+ than the general online population include Bowling Green, Kentucky, Portland, Oregon, and Bend, Oregon.

New data from Experian Hitwise shows that Google+ is growing fast, thanks to a young demographic and lots of traffic from other Google properties. The web analytics firm has released its first set of data regarding Google's new social network. Although the data only extends to July 16, it provides a detailed picture into the numbers that are driving Google+'s growth. Here are some of the most interesting stats from Experian Hitwise's report:The truth of the matter is that none of these stats are official and Google+ is still very new -- so it's anybody's guess as to how accurate these figures are. Still, we think the company's numbers make sense. While Google+ is gaining in popularity, it is still minuscule compared to Facebook, Twitter, Zynga, Tagged or even MySpace. Google's Facebook competitor may have 18 million users , but it still has a lot of room for growth.