The Massachusetts Pension Reserves Investment Trust Fund earned the top rate of return from its PE portfolio with 15.4 percent annualized returns over 10 years.
Other top pension PE players over the same period were the Teacher Retirement System of Texas (15.5 percent); the Houston Firefighters' Relief and Retirement Fund (13.6 percent); the Minnesota State Board of Investment (14.4 percent); and the Iowa Public Employees' Retirement System (14.1 percent).
(Read more: Private equity-backed M&A having strongest year since 2007)
"We're delighted. It's a testament not only to the current staff, but to the legacy of those who launched and built a long-term track record second to none," said Michael Trotsky, executive director and chief investment officer for the Massachusetts pension.
"Private equity is an important asset class. It provides diversification and has been a leading contributor to our high returns since the mid-1980s."
Trotsky said the pension has about 10 percent of its money in PE—around the national average for large public retirement funds—and has no plans to change that. The state used 103 different PE firms as last year, including The Blackstone Group, Kohlberg Kravis Roberts and Bain Capital.
(Read more: Private equity's growing play: Africa)
The PEGCC study also ranked pensions with the largest allocations to private equity.
The biggest is the California Public Employees'Retirement System, with $34.2 billion invested. Other huge allocators include the California State Teachers' Retirement System ($22.6 billion); the Washington State Department of Retirement Systems ($16.1 billion); the New York State and Local Retirement System ($14.9 billion); and the Oregon Public Employees Retirement System ($14.1 billion).
"Time and again private equity has proven that it's the single best asset class for public pensions, by delivering superior returns over long time horizons," Steve Judge, president and CEO of the PEGCC, said in a statement.
"Private equity continues to strengthen the retirement security of the millions of American police officers, firefighters, teachers and administrators who rely on hard-earned pension benefits. There is no doubt that private equity returns are essential to improving the pension funding equation."