Hi @mgoose
You can definitely do this! You will want to set up shipping zones within your shipping profile that you are using for your products.
Most likely you have all your shipping zones (the places you ship to) grouped together. You will instead want to separate out the USA or the specific states you want the free shipping zone to be available for. Make sure to also include your standard shipping rates in each of the zones as well.
You can read more about setting up your shipping rates in our Help Center here: Setting up shipping profiles · Shopify Help Center
If you need additional help with setting this up our live support team would be more than happy to help.