The independent workforce grew 12% over the past five years, reaching close to 18 million full-time independent workers in 2015, according to the first release of data from MBO Partners’ 2015 State of Independence in America research. This compares to 7% growth in overall employment over the same five-year period. The research forecasts the trend will continue, as four in five independents reported they plan on staying independent and one in seven non-independents plan to join that group in the coming years.

In addition to the full-time independents, 12.5 million “side-giggers” take on part-time independent work, the report found.

High-earning independent workers now represent 10% of all independents and are the fastest-growing segment. The number of independents earning $100,000 or more per year rose 45% over the last five years to 2.9 million people.

“As this first look at the State of Independence research shows, the independent workforce is a rapidly growing population of high-income professionals,” said MBO Partners Founder and CEO Gene Zaino.  “Nearly 18 million Americans are independent workers, and with 79% saying they are happier working independently than in traditional jobs, we expect this trend to continue.”

With multiple revenue streams from an average of four or more clients, four in 10 workers said they feel more secure working independently than in a traditional job.

MBO Partners provides back-office services for independent consultants and contractor management services for companies. The MBO Partners State of Independence series is based on more than 14,000 in-depth surveys of independent workers since 2011. The full State of Independence Report, with additional findings tracking five years of data on the independent workforce, will be released in the fall.

This article has been corrected. The original version said the number of independent workers earning $100,000 or more is 2.4 million people.