Scott Walker fired off 13 tweets on July 26, 2015 that cite accomplishments and highpoints during his time as Wisconsin's governor.

This was one of them:

"Overall bonding in latest WI state budget is at 20 year low. State pension system is only one fully funded in the country."

We decided to check the second part of the statement to see if anything has changed since we first rated it True in 2013. The fully-funded pension system is also a prominent talking point for Walker in his quest for the Republican presidential nomination.

Where pension benefits come from

The Wisconsin Retirement System provides retirement, disability and death benefits not only to all state employees, but to nearly all local government employees in Wisconsin. With some $85 billion in what are known as actuarial assets, it covers more than 256,000 active public employees, including teachers and municipal employees, plus 154,000 retirees and others who are no longer active employees.

The funds come from three sources: employer contributions, employee contributions and investment earnings. The employer-employee split was changed dramatically by Act 10, Walker's 2011 collective bargaining reform law.

Before Act 10, the state, as well as the local governments participating in the state retirement system, had agreed to make almost of the contributions that employees were required to make toward their pensions. In other words, often as a result of union bargaining, the employers were making the employer contributions to the pension fund and nearly all of the employee contributions, as well.

In 2010, for example, state and local government employers made 99 percent of the employer-employee contributions to the system. As of 2013, the latest figures available, employers paid 57 percent and employees 43 percent.

So, just how healthy is the pension fund, and how does it compare?

How close to fully funded?

The state's most recent actuarial evaluation showed that as of the end of 2013, the retirement system was in balance. That is, the expected total retirement benefit obligations equalled the assets ultimately expected to be available to the system. More specifically, the Gabriel Roeder Smith & Co. firm said the pension fund was 99.96 percent funded.

It’s worth noting the actuarial reports have shown the retirement system funding at 99 percent or greater not only during Walker's tenure, but dating back to 2003. Wisconsin's pension system has long been viewed as a national model.

When we rated Walker's 2013 claim that Wisconsin’s pension fund was the only fully funded one in the country, we relied primarily on a report from the non-partisan Pew Charitable Trusts. It was since updated, with the most recent version published in July 2015.

That report shows that in 2013, South Dakota's pension system had joined Wisconsin as being fully funded. Pew actually ranked South Dakota first and Wisconsin second, even though both were 99.9 percent funded.

The national average was 72 percent. Illinois was lowest, at 39 percent.

Another report -- which included some actual as well as estimated data for 2014 -- also listed South Dakota and Wisconsin as the only fully funded pension systems.

That report, from the Center for Retirement Research at Boston College, estimated that Wisconsin had an asset-to-liability ratio of 104 percent for 2014, up from 99.9 percent in each of the three previous years.

Actual data for South Dakota, meanwhile, showed that state's pension system was funded at 100 percent in both 2013 and 2014.

(The report also examined local pension plans. The City of Milwaukee's was estimated at 100.8 percent funded in 2014.)

Keith Brainard, research director for the National Association of State Retirement Administrators, told us Wisconsin and South Dakota are well funded because their investments have performed well and their retirement benefits "have remained fairly reasonable." In addition, in Wisconsin’s case, retirement benefits go down when investments don’t perform up to par, he said.

Our rating

Walker says Wisconsin's "pension system is only one fully funded in the country."

That was the case among state pension plans in 2012, but newer reports show slightly different results. According to Pew Charitable Trusts, both South Dakota and Wisconsin were fully funded in 2013; and according to Boston College, both were fully funded in 2013 and 2014.

We rate Walker’s statement Mostly True.