Magento 1.9 CE – Disable State/Province Select

• First,your block class should extend Block class Mage_Directory_Block_Data. bcoz of this class generate country dropdown for using function getCountryHtmlSelect()

Then add region and country dropdown using below code at your phtml file

  <li class="fields">
                    <div class="field">
                        <label for="region_id" class="required"><em>*</em><?php echo $this->__('State/Province') ?></label>
                        <div class="input-box">
                            <select id="region_id" name="region_id" title="<?php echo $this->quoteEscape($this->__('State/Province')) ?>" class="validate-select" style="display:none;">
                                <option value=""><?php echo $this->__('Please select region, state or province') ?></option>
                            </select>
                            <script type="text/javascript">
                            //<![CDATA[
                                $('region_id').setAttribute('defaultValue', "");
                            //]]>
                            </script>
                            <input type="text" id="region" name="region" value="" title="<?php echo $this->quoteEscape($this->__('State/Province')) ?>" class="input-text <?php echo $this->helper('customer/address')->getAttributeValidationClass('region') ?>" style="display:none;" />
                        </div>
                    <div class="field">
                        <label for="country" class="required"><em>*</em><?php echo $this->__('Country') ?></label>
                        <div class="input-box">
                            <?php echo $this->getCountryHtmlSelect() ?>
                        </div>
                    </div>
                </li>

• Now,you need add some javascript code which will change region dropdown using below code:

new RegionUpdater('country', 'region', 'region_id', <?php echo $this->helper('directory')->getRegionJson() ?>, undefined, 'zip');

This is with reference to chat.

as you are using custom theme which have made changes in billing.phtml which breaks a default functionality of magento. compare the file with default theme RWD package and find out the unwanted code from it and make sure that all default id's and form's must be present their.

remove unwanted scripts from the code.

Hope this will help you.