According to the Civilization V's website, the demo is soon to be announced! Rarely do I decide to cut straight to the chase, however this is some pretty exciting stuff here. The Civilization series is one that has held a lot of very fun (and time consuming) moments for gamers, and is a nice break from the typical strategy game.
The demo will be landing in September, sometime before the full game is released. The exact release date has yet to be announced, but no doubt the devs will give us plenty of time to wrap our minds around how awesome this game will be.
This year is definitely a fantastic time to be a PC gamer, that's for sure.
Source: Civilization V