The number of US independent workers will grow to just under 40 million in 2019 from approximately 30 million today, according to a new study by MBO Partners, a provider of management systems for independent professionals and clients that engage them.

Independent professionals are defined in the report as people who work in nontraditional, nonpermanent full- or part-time employment and who “identify themselves as consultants, freelancers, contractors, solopreneur and on-call workers, among others.”

Independents live and work in all 50 states; four in 10 live in urban or close-in suburbs, 30 percent in outer suburbs and another 30 percent in small towns or rural areas. The also come from all age groups: 28 percent Millennials, 29 percent Gen X, 30 percent Boomers and 14 percent Matures.

The survey found 82 percent are highly satisfied or satisfied with their work style, and only 7 percent were dissatisfied.

The annual study by MBO also divided independent workers into two groups: “soloprenuers” who work 15 hours or more per week and “side-giggers” who work as an independent worker less than 15 hours per week.

Soloprenuers numbered 17.9 million in this year’s survey, up from 15.9 million in 2011. They generated about $1.1 trillion in total income in the past year. And most soloprenuers had more than one revenue-generating activity.

Side-giggers numbered 12.1 million. Fifty-eight percent of side-giggers worked independently primarily to supplement their income.

“Our study reveals independent work is far from a one-size-fits-all story,” said Gene Zaino, CEO and president of MBO Partners. “With shades of independence — from solopreneurs to side-giggers — there is a clear need for a variety of workforce solutions. The study is a wake-up call that at 30 million strong and forecast to grow to 40 million, the independent workforce is not just here, but here to stay.”

The report is based on two online surveys conducted in May of 2014. One included 2,017 responses from residents of the US, which was used to size the independent workforce and define the interest in becoming an independent worker by the general population. The other included 1,109 responses from independent workers to profile their motivations and characteristics.