Mariah Carey and James Packer -- Celebrating Red, White and You! (PHOTO)

Mariah Carey finally got billionaire James Packer on her turf -- Las Vegas -- just in time for the couple's first 4th of July together.

They shut down the rooftop deck of the swanky Mirage Villas for a Saturday evening celebration. We're told James dropped THOUSANDS to rent out the whole joint for Mariah, her managers, and Brett Ratner. This is the first time they've been together back in the States since Packer started courting Mimi during their Mediterranean tour aboard his mega yacht.

On the flip side ... Nick Cannon shared a meme addressing his single status captioned "I'm dating me."

To each his own ...