They last published Hector: Badge of Carnage in 2011, but that was apparently actually co-developed by them. Telltale designers Dave Grossman and Mark Darin are credited with design on episodes 2 and 3.
The Jackbox Party Pack appears to be a completely different situation altogether, as The Jackbox Party Pack was already developed and published digitally by Jackbox Games. Telltale is simply handling publishing duties once it comes out on disc on November 10th.
This definitely shows how far Telltale has grown, as even after the success of The Walking Dead, they still had some of their own games published on disc by other publishers. Law & Order: Legacies was published on disc for Windows by Avanquest Software in November 2012, shortly before the release of the final episode of The Walking Dead: Season One. They are now large enough that they publish all of their titles on computers and consoles, and now have begun publishing games developed by other companies as well.