Counties are regions within a State in the USA.  Some Counties require that Taxes need to be collected on a County level rather than just at the State Level.

Any shop which has defined taxes at the County level will find that County must be selected at Checkout.  The reason is because in order to calculate Tax (which is done at this point), the customer must select the County.

To remove the County from Checkout, taxes need to be defined at a State Level only. Caution: This is not recommended if you have to collect Taxes at a county level

Here is an example to Illustrate, tax rates are factious and for illustration purposes only.

1. I am located in Orange County in the State of California and I ship all over the world.

2. I must collect 2% tax for any customer that purchases products from my store if they are located in my county - Orange.

3. I must collect 5% tax for anyone who purchases products from my store if they are located in the State of California (my State).

4. Anyone located located in California pays 5% tax and anyone in Orange county pays 5% tax plus and additional 2% county tax.

5. Anyone located outside California pays not tax at all.

6. I charge a flat rate of postage of $10 per order regardless of location and it includes Tax

I set my shop up as follows:

California State tax 5% which applies only to California - Click the radio button "USA/California" when defining this tax.

Orange County Tax of 2%. Click the radio button "United States, California, Orange" to add this tax.

So Now at Checkout It shows like this. Customers who are located in California but not in Orange county must choose Other for their County and only the State tax applies. 

At Checkout Customers who are located in Orange County must choose Orange in the list and two taxes will apply, California State Tax and Orange County tax 

Customers outside California do not pay tax and see the following at checkout, they do not have to select County: 

If you do not want to display County at Checkout then you must setup only State Taxes that apply at the state level only (in this example California) - again this is not recommended if  you have to collect County taxes. Please check with your Authorized tax agent regarding this.