Most private campgrounds have WIFI service for web surfing, etc., but they aren't secure - so don't use them for banking or if you plan to use a credit/debit card to charge something. For that, I use a WIFI Hot Spot. All of the major cell phone carriers offer them, and they use the same over-the-air signal as a cell phone. Verizon sells one that is very popular and has the widest service coverage. But it's pretty pricy for both initial purchase and for data use. Trac-Fone also offers one that is a lot less expensive. I went with "Smart-Talk". It is Walmart's proprietary version - serviced by Trac-Fone. And just like Trac-Fone's phones, it is "pay as you go" - using cards that supply various amounts of data for a specified period of time (1 or 2 months). It uses Verizon's network, so coverage is virtually nation wide, but it's a LOT less expensive than Verizon. Of course, you can only purchase the Hot Spot and the data cards at Walmart, but Walmarts are pretty easy to find. You can also renew service over a phone, using a credit card to pay for it.
One of the things I like about their service is that you can buy service cards in several service levels - ie. 2 GB/1 month service for $25, 5 GB/2 months service for $50, 7GB/2 months service for $75, etc. During the winter, I stay at a private campground that has public WIFI service, and I only use my hot spot for banking. So, I only buy the 2 GB/1 month card. But during the summer (when I'm hosting at Michigan State Parks that don't have WIFI service), I use my hot spot for all my internet use - so I buy the 5 GB/2 month plan. One thing I might mention is that once you buy the service card, you actually use a phone to initialize it into the WIFI Hot Spot. That means, you need cell phone service. And if you're out in the boonies, you may have to travel around to get that. But then again, you'll have to find a spot where you can get WIFI service anyway.
Another option is to use your smart phone as a WIFI hot spot. I don't use a smart phone, but I'm told "There's an APP for that"!
Hope this info helps you out. Safe travels and happy camping!