According to a recent Pew Research Center study, 11% of U.S. adults still don't use the internet. That's a significant change from 48% in 2000, but the study revealed that age remains a major factor, with 34% of senior citizens remaining offline.

Nonetheless, seniors are more connected than ever. Eighty-six percent of seniors were offline in 2000, but easier-to-use apps and sites -- particularly Facebook -- brought them online. Pew recently reported that 55% of Americans over the age of 50 use Facebook.

Age isn't the only factor that impacts internet use. Income is another major variable, with 19% of Americans earning less than $30,000 annually staying offline, compared to single-digit percentages for all other income brackets.

Internet use also varies by education and location. Far higher percentages of Americans with lower education levels and those who live in rural areas are offline compared to college-educated urban and suburban folks. This suggests that while the U.S. has one of the highest internet penetration rates in the world, some people are still being left behind.