The U.S. government is the nation’s largest property owner – 42 million acres of land and nearly three billion square feet of real estate, if the latest data from the Federal Real Property Council (FRPC) can be trusted. The problem is, according to a recent GAO report, the FRPC’s data can’t be trusted. And this raises all sorts of issues, not the least of which is that the government doesn’t even know how much unused property it owns.

As reported by NPR, the FPRC lists nearly 80,000 properties that are either completely unused or sorely under-utilized. If these numbers are correct, this unused property could be costing taxpayers upwards of $1.7 billion in annual upkeep costs.

But as the GAO report points out, the FRPC’s data is so unsound that it’s difficult to verify how accurate it is. GAO inspectors visited 26 sites on the FRPC’s list, and found inconsistencies or inaccuracies in the reporting on 23 of them. Vacant buildings were incorrectly coded as occupied, and vice-versa. Partially demolished buildings were listed as 100% sound.

Given the inaccuracies in the data it’s difficult to get a clear sense of where the underused buildings are, or what agencies they belong to. But other government datasets can shed some light on the issue. In 2010 and 2011 the White House made a push to dispose of “excess” federal properties – which it defines as property no longer needed by the government - as a cost-saving measure. They published their 2011 dataset, which contains a list of excess properties as of that year.

Among other things, the dataset shows that the USDA holds the most excess properties of any federal agency – over 3,500 of them. Nearly all of these are forest service buildings in national forests, and many of them are in Western states like California and Colorado. The Navy is another major holder of excess real estate – over 2,000 properties.

The data also provide a state-level breakdown of where excess properties are located, although military properties are excluded from this list due to potential security concerns. The geographic distribution of unused real estate tilts westward, with California leading the pack, followed by Washington state. Much of this is likely a reflection of the USDA’s holdings in national forests, which are more prevalent out West.

It’s tough to say for certain where the government goes from here. The GAO report rather archly notes that federal efforts to achieve cost savings associated with better property management are in a state of limbo – “some of these efforts have been discontinued and the potential savings for others are unclear.” It also hints at some intra-agency disagreement over the true extent of the problem: “OMB agreed that real property challenges remain but raised concerns about how GAO characterized its findings. GAO believes its findings are properly presented.”

At any rate, with the potential for billions of dollars in annual savings on the table it’s hard to imagine why Congress would turn a blind eye to the issue for much longer.