The Biebers finally sent out their save the dates, and TMZ got a sneak peek at the comic book-style card announcing their 2nd nuptials. It's short on specifics -- this isn't the formal invitation -- but says the ceremony and party are going down Sept. 30 in South Carolina.

You'll recall ... this is Justin and Hailey's 4th attempt to get their wedding party on the books -- and it looks like the couple has finally settled on a time and place to pull the trigger.

Now, on the face of it, ya think ... what gives? Justin and Hailey have no special connection to the Palmetto State. The Biebs has nothing but Canadian roots, and of course, the Baldwins are New Yorkers through and through.

So, it appears their choice boils down to nothing more than -- WE LIKE THIS PLACE!!!

Justin and Hailey were spotted last week around Palmetto Bluff -- a gorgeous waterfront area on the May River, which is a major tourist attraction. Bieber's also been there before, on tour and otherwise, and seems to dig it.

The southern charm must have rubbed off on Hailey too. Truth is, South Carolina's known for stunning wedding venues, so it's not as odd a venue as you were thinking.

Here's another little nugget we found -- our sources tell us party planner to the stars, Mindy Weiss, is putting the Biebers' shindig together. She's done events for the Kardashians, Heidi Klum, Ellen DeGeneres, Ciara, Diana Ross, Katy Perry ... and tons more.