Yes, they exist. Or at least they used to. No one knows for a fact (apart from 30 degree+ masons) if they still exist. The government banned them in the 1700's. But the symbolics in a lot of todays TV advertisements would tell us that the Illuminati have done what they wanted to do back when they were first formed. They formed as a group of political activists (ironic) to take over the government, that way they can control everything themselves. Now, if they're still a real organisation, they're only doing this for control, wealth and ownership of the general public.
As I said, its anyone's guess whether they ARE still in existence, but anyone who denies that they used to exist, hasn't really searched for them, or they're hiding it.
But, tbh, it ain't really a big deal. Whether they exist or not is irrelevant as Politics is just as corrupted as it always has been. It's never going to change.