There are now more than 500 million devices in US homes connected to the Internet. Furthermore, the average number of devices per US Internet household has grown from 5.3 devices just three months ago to 5.7 today.

The latest findings come from The NPD Group, which surveyed more than 4,000 US consumers 18-years-old and up. The firm defines an Internet-connected device as one that delivers applications such as “computers, tablets, smartphones, HDTVs, Blu-ray Disc Players, video game consoles, and streaming media set top boxes.”

The firm apparently refers to “apps” as software in general, as opposed to devices with access to an app store. While I would normally refer to gadgets with apps as anything running Android, iOS, BlackBerry, Windows 8, or Windows Phone, it’s clear the term has expanded to almost any device that a consumer can buy, but I digress.

NPD says PC penetration among US Internet connected households this quarter is “nearly ubiquitous at 93 percent” but was “virtually unchanged” over the last quarter. An increase in mobile devices naturally helped the US market to hit the new milestone: smartphone penetration rose from 52 percent to 57 percent of cell phone users while tablet penetration increased significantly from 35 to 53 percent of Internet households.

Here’s a more visual representation of the top three categories:

CI March182013 NPD: US homes now hold over 500m Internet connected devices with apps, at an average of 5.7 per household

“Even with this extraordinary growth in the smartphone and tablet market, PCs are still the most prevalent connected device in U.S. Internet households, and this is a fact that won’t be changing any time soon,” John Buffone, director of devices at NPD Connected Intelligence, said in a statement. “However, when you look at the combined number of smartphones and tablets consumers own, for the first time ever it exceeded the installed base of computers.”

Converting those percentages into raw numbers, the install base of smartphones increased by some 9 million while tablets gained nearly 18 million in the last three months. Unsurprisingly, Apple and Samsung remained the most prevalent smartphone brands owned by US consumers, and Apple continued to dominate the tablet market.

See also – Apple passes Samsung to become top US mobile phone vendor with record 34% market share: Report and comScore: Apple debuts 2013 as top US smartphone maker, Samsung gains but Android falls for the first time

Top image credit: Jung Yeon-Je/Getty Images