Is it illegal to lie about how many people are going to share a hotel room?

If I go to a hotel (Motel 6) and ask for a room for the night and tell them it is just me but really my friend is going to meet me there later can I get in some kind of trouble for that?

If so how do they find out?

You would be charged for an additional person, so technically it is theft. However, it goes on all the time. Why not just pay the extra?

well, normally they allow two people in the room anyway, or even 3. It matters when you get like 6 in a one bedroom, then you really should be paying for more rooms. They might kick you out.

But in you're situation, it doesnt matter

Yeah, I wouldn't do that. That would probably be the lamest crime on the face of the earth. Don't do that to yourself man.

Maybe if you said 1 and brought like 10, that would result in something cool, but otherwise, no.

It is unethical and rude. The most that could happen to you is that you get kicked out or you have to pay for the extra people and also get kicked out.

Some states have a law for things of that nature. It's called "defrauding an inkeeper".