If the majority of your customers are from a specific state and/or country, it is possible to set a default country and/or state for your customers' address. These default values will be applied for the customers' address and, if enabled, for their billing address.
1. Go to Settings>Customer details
2. In the Standard fields tab, in the Default Values section, from the Country  and State/Province  scroll down menus, set a default country and/or state for your customers' address.