Do I need to let my insurance company know that I won't be renewing my policy?

To be safe, call them. You don't want them to have some bizarre cancellation fee or something. That's probably not the case, but just for piece of mind I would do it. Now with that said, don't let them con you into renewing it with them. You have no obligation.

you should call them and tell them you won't be renewing..

On time, I didn't call a company (Prudentual) and let them know i wouldn't be renewing. Well, I always paid the entire policy in one payment, so they automatically renewed me and sent the bill. Who would've ever dreamed they would renew without payment? Anyway, I owed them for 14 days of prorated insurance. What a *****! Call em.

You can just let it expire. When they don't receive payment, they will get the hint. You could also try informing them that you're canceling, and they might try and offer you a better rate to save your business.

If you don't pay them they will get the message, but a call would be a nice thing to do.

You raise some good points in your question.