Jon Gosselin Tax Lien -- Proud Father ... of a 3-Year-Old Tax Lien

Jon Gosselin became a free man in 2009 -- problem is, he allegedly snubbed the State of Pennsylvania in the process ... and now, the schlubby reality dad's been hit with a $39K tax lien.

If you recall, 2009 was the year Jon and Kate went splitsville ... scoring them both more publicity -- i.e. paid interviews and appearances -- than either could've imagined.

But according to docs filed in Berks County, Pennsylvania ... Jon still failed to dish out the necessary cash to the government that year ... resulting in the massive tax bill.

Let's hope he saved some of that sweet reality cash ... 'cause while the bill might've been a doable amount back then, it's gonna be a pain in 2013 ... considering Jon works a totally normal person job now.