Members of the baby boom generation make up one-third of the independent workforce, according to estimates released this week by MBO Partners. The number of baby boomers who are independent workers totals 5 million.

MBO Partners defines independent workers as people who work at least 15 hours a week in non-traditional, nonpermanent employment, including consultants, freelancers, contractors, self-employed and on-call workers among others.

Survey data on boomer independent workers found that 59 percent chose to be independent, according to MBO Partners. Seventy percent are highly satisfied with being independent.

Seventy-nine percent of boomers cite the freedom that independent work offers as they key benefit. Sixty-six percent of boomer independent workers are college educated. The median annual income of boomer independents is $77,000.

“In the face of recent financial uncertainty and a tumultuous job market, many in the boomer generation have turned adversity into opportunity and taken charge of their lives by working independently,” said MBO Partners CEO Gene Zaino. “MBO Partners has had a front-row seat to the rise of boomer independents — our own MBO Partners community spans all workforce generations, but over-indexes with baby boomer professionals.”

MBO Partners expects the number of boomer independent workers to rise by 1.2 million in the next two years.

MBO Partners’ data comes from two online surveys conducted in July 2011. One survey included 1,144 U.S. residents and was used to size the independent workforce and define the interest in becoming independent workers by the general population. The other survey included 601 independent workers and was used to profile their characteristics and motivations.

MBO Partners provides business services to independent contractors as well as independent contractor compliance and payrolling services for staffing buyers.