Cash and security holdings by the 100 largest public pension funds in the U.S. reached record levels of nearly $3 trillion in the second quarter, according to the Census Bureau's monthly report released Monday.

The Census Bureau said aggregate holdings of the 100 funds rose 8.4 percent year over year to $2.943.5 trillion, the highest level since the bureau started keeping track in 1968 and completing a comeback from the depths of the Great Recession. The previous high was in 2007 before the 2008 market crash. Investments in the funds generated $38.3 billion in the second quarter, a gain of 0.4 percent.

The increase comes as public pensions funds are coming under increasing pressure to institute reforms to meet unfunded liabilities. Recent changes to calculating future payments have significantly raised that target number. Pension systems like California's, the nation's largest, and Detroit's, where municipal bankruptcy has thrown retiree benefits in doubt, have been wrestling with how to ensure solvency.