One-third of all adults in the United States own smartphones, according to new research released Monday from the Pew Internet Project.

The Pew survey found that 33 percent of respondents with cell phones said they owned a smartphone, with 39 percent reporting their phone ran on an operating system such as Android, iOS or BlackBerry.

Android accounted for 35 percent of all smartphone owners, while iPhone and BlackBerry tied at 24 percent each. Another 4 percent of smartphone owners reported they owned a Windows phone, and 6 percent described their phone as a Palm device.

In terms of demographics, Android phones were more commonly used by young adults and African-Americans, while iPhones and BlackBerry devices are most prevalent among college graduates and affluent adults.

The survey also found a growing dependence on smartphones to as the main way of getting online. One-quarter of smartphone owners surveyed said they used their device as the primary means of accessing the Internet, despite having other means of online access at home. Of those who mostly used their smartphones to get online, roughly one-third lacked a high-speed broadband connection at home.

Smartphone ownership was found to skew heavily toward urban populations, with just 5 percent of rural cell phone owners reporting they owned an iPhone, compared to 10 percent of suburban smartphone owners and 12 percent of urban smartphone owners.

The data on smartphone use from the Pew Internet Project was based on a survey of 2,277 adults conducted in April and May. The margin of error for the results based on smartphone owners is +/-4.5 percentage points, and the margin of error for results based on all cell phone owners is +/-3 percentage points.