Pew Research Center has published a wide-ranging survey on device ownership amongst American adults, revealing detailed demographic breakdowns of a variety of different electronic gadgets which can play video games.
The top-line data is this: 68 percent of U.S. adults own smartphones; 45 percent own tablets; 73 percent own PCs; 40 percent own game consoles; and 14 percent own portable consoles.
Now, how game-capable all of these devices are was not measured; PCs, tablets, and phones can easily age out of relevance, and the "portable" segment apparently included devices such as this neo-retro Sega Genesis handheld, judging from Pew's wording, which is irrelevant to developers who might be considering making a 3DS game.
Also of note is that under-18s, who buy and play a lot of games across a variety of platforms, are not included in the research. If you're interested in a detailed breakdown of device ownership amongst American adults, however, it's worth the time to take a tour through the data.