American tax filers made roughly $192 billion in interest-free loans to the federal government last year, according to IRS data just released by the Brookings Institution. All told, 80 percent of tax filers overpaid on their taxes and received refund checks from the IRS for tax year 2012, with the average refund worth $2,742. In effect, those are a zero-interest loans to Uncle Sam.

The sum of $192 billion is huge. To put in perspective, that's more than a quarter of the federal budget deficit last year. For a country that gripes as much about taxes as we do, it's frankly incredible that so many of us willingly overpay our taxes year after year.

Where are people most likely to overpay (and get refunds)? Appalachia and the deep South stand out in the map below. This is partially related to poverty rates -- people at the lower ends of the income spectrum have much lower tax burdens, due to lower overall rates and tax breaks like the Earned Income Tax Credit. Overall, Chattahoochee County, Ga., takes home the prize for the highest share of filers getting refund checks -- 95 percent, to be exact. At the other end of the spectrum lies Liberty County, Mont., where only 38 percent of tax filers got refunds.

We can also come at this data from the other direction: Where are Americans underpaying their taxes? Fifteen percent of all tax filers had a balance due this year -- among this crowd, the average amount owed was $4,656. The county-level map for this subset of filers is basically the inverse of the previous one. The highest concentration of people owing on their taxes occurs in the Plains states, and to a lesser extent, certain coastal metropolitan areas.

Brookings's Elizabeth Kneebone notes that these counties "tend to have higher than average shares of taxpayers who filed schedule C, E, or F. So they are more likely to be home to filers who are self-employed or who are declaring a profit or loss from farming (or other supplemental income sources)."

Finally, if you've been paying close attention you'll note that after overpayers and underpayers are tallied, there are still roughly 5 percent of taxpayers who we haven't accounted for. These near-mythical creatures are the folks who heeded the scolding of business columnists everywhere and saw to it that their tax payments zeroed out perfectly at year's end -- no money due, no money refunded.

This map looks similar to the previous one -- again there's a relatively high concentration of these filers in the upper Plains states. Many of them are likely to be self-employed or farmers who are exceptionally good at estimating their taxes. But states like Michigan, Pennsylvania and Vermont stand out as regions were relatively high percentages of filers are breaking even. Again, Chattahoochee County, Ga., and Liberty County, Mont. are the alpha and omega of this subset of filers: Liberty County boasts the highest share of break-eveners at 32 percent, while only 0.8 percent of Chattahoochee residents did the same.

Doubtless it would be better for all of us if we followed Liberty County's example and scrupulously monitored our taxes to make sure we break even at year's end. But if you've ever tried to do this you know that it's really, really hard. A single-digit change to your W-4 can cause your final tax balance to vary by thousands of dollars. It seems that most Americans would prefer to play it safe, err on the side of overpayment, and ensure they get that gratifying refund check at the end of the year. Sure, it's bad personal finance -- but if Donald Rumsfeld can't figure it out, what hope do the rest of us have?