I just asked my insurance company about this. It depends on the venue and the people who own it. If you own your home and you have homeowner’s insurance, which you should, you should be able to get an event rider on your policy which would cover any venue in which your are hosting your wedding.
I rent, and only have renter’s insurance, and I was quoted $50 for a $1 million dollar event rider. And even if I choose not to go that route, I still have $300K worth of liability insurance, which is a part of my regular policy, in case of an incidents (God forbid!).
By the way, these rates are most likely higher/lower depending on your location. We’re in North Central PA.
Most venue owners will tell you when you inquire about booking if you need insurance, and exactly how much insurance you need. Also, they will request proof of said insurance from your insurance company. I just had my agent fax a copy of my policy to my landlords.