Magento’s region ID’s are internal primary keys on the database that don’t mean anything to the rest of the world.  two digit state codes, such as MN or AL are a universal region identifier.

I had to import customers from an external ERP into Magento 2.  There might be a way to set a region on a customer using the two digit code, I just wrote a simple way to get the region ID from the state code.

Here is the helper I wrote for this.  Pretty straight forward.

<?php

/**
 *
 * @author Kevin Miles <kevin.miles@evermore.tech>
 */

namespace Evermore\CustomerImport\Helper;

class Address extends \Magento\Framework\App\Helper\AbstractHelper
{
    protected $_regionFactory;

    public function __construct(
        \Magento\Framework\App\Helper\Context $context,
        \Magento\Directory\Model\RegionFactory $regionFactory
    ) {
        $this->_regionFactory = $regionFactory;

        parent::__construct($context);
    }

    /**
     * Gets the region ID from the two digit state code.
     * @param $state - Two letter state code
     *
     * @return int|bool
     */
    public function getRegionCode($state, $countryId = 'US') {
        try {
            $region   = $this->_regionFactory->create();
            $regionId = $region->loadByCode( $state, $countryId )->getId();
            return $regionId;
        }
        catch(\Exception $e) {
            $this->_logger->critical($e->getMessage());
            return false;
        }
    }
}

Here is the code that creates the customer address.

<?php

/**
 *
 * @author Kevin Miles <kevin.miles@evermore.tech>
 */

namespace Evermore\CustomerImport\Helper;

class CustomerCreate extends \Magento\Framework\App\Helper\AbstractHelper
{
    protected $_customerFactory;
    protected $_addressFactory;
    protected $_addressHelper;

    public function __construct(
        \Magento\Framework\App\Helper\Context $context,
        \Magento\Customer\Model\CustomerFactory $customerFactory,
        \Magento\Customer\Model\AddressFactory $addressFactory,
        \FEvermore\CustomerImport\Helper\Address $addressHelper
    ) {
        $this->_customerFactory = $customerFactory;
        $this->_addressFactory = $addressFactory;
        $this->_addressHelper = $addressHelper;
        parent::__construct($context);
    }

    public function createCustomer($customer = array()) {
    
        $newCustomer = $this->_customerFactory->create();
        $newCustomer->setWebsiteId(1);  //Main website.
        $newCustomer->setGroupId(4); //Group ID of your group
    
        $newCustomer->setFirstname($customer['firstname']);
        $newCustomer->setLastname($customer['lastname']);
        $newCustomer->setEmail($customer['email']);
        $newCustomer->setPassword('P@ssw0rd');
        $newCustomer->save();
    
        $address = $this->_addressFactory->create();
        $address->setCustomerId($newCustomer->getId())
                ->setFirstname($customer['firstname'])
                ->setLastname($customer['lastname'])
                ->setCountryId($customer['country'])
                ->setStreet($customer['address'])
                ->setCity($customer['city'])
                ->setRegionId($this->_addressHelper->getRegionCode($customer['state']))  //This is where i get the region id.
                ->setPostcode($customer['zip'])
                ->setTelephone($customer['phone'])
                ->setFax($customer['fax'])
                ->setSaveInAddressBook(1)
                ->setIsDefaultBilling(1)
                ->setIsDefaultShipping(1);
        $address->save();
    }
    
}