The Pew Research Center's Internet & American Life Project said the percentage of high-speed users represented a small but statistically significant rise from the 66 percent of adults who said they had home broadband in April 2012.
The percentage using dial-up as of May 2013 has held steady at three percent for the past two years, Pew found, but is down sharply from a peak of 41 percent in 2001.
Overall, 85 percent of Americans use the Internet, the report said. Of those who lack a high-speed connection at home, 10 percent have smartphones that can access the Web.
As previous research has found, those with the highest rates of home broadband use continue to be college graduates, adults under age 50, and adults living in households earning at least $50,000 per year. Whites and adults living in urban or suburban areas also had above-average rates.
"We've consistently found that age, education, and household income are among the strongest factors associated with home broadband adoption," said Kathryn Zickuhr, research associate for Pew and lead author of the report.
"Many dial-up users cite cost and access as the main reasons they don't have broadband, but for adults who don't use the Internet at all, a lack of interest is often the main issue."
The survey notes that more than half of all American adults own a smartphone, but it did not determine whether this constitutes "broadband" speed.
"Broadband users can consume and create many types of content in ways that dial-up users cannot, and our research has long shown major differences in these two groups' online behavior," said Pew's Aaron Smith, a co-author of the report.
"Smartphones may offer an additional avenue for Internet access that surpasses the dial-up experience in many ways, but those who rely on them for home Internet use may face limitations that are not shared by those with traditional broadband connections."
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