From http://jsfiddle.net/hrHWJ/ State dropdown conditional on Country dropdown

StateCountry

<script type="text/javascript" src="https://ajax.googleapis.com/ajax/libs/jquery/1.7.2/jquery.min.js"></script>
<script type="text/javascript">

    jQuery(document).ready(function($){

        /*The country onchange starts here*/
        var orig_html;
        var orig_value;
        var state_value;

        var us_states = {AL: 'Alabama', AK: 'Alaska', AZ: 'Arizona', AR: 'Arkansas', CA: 'California', CO: 'Colorado', CT: 'Connecticut', DE: 'Delaware', DC: 'District of Columbia', FL: 'Florida', GA: 'Georgia', HI: 'Hawaii', ID: 'Idaho', IL: 'Illinois', IN: 'Indiana', IA: 'Iowa', KS: 'Kansas', KY: 'Kentucky', LA: 'Louisiana', ME: 'Maine', MD: 'Maryland', MA: 'Massachusetts', MI: 'Michigan', MN: 'Minnesota', MS: 'Mississippi', MO: 'Missouri', MT: 'Montana', NE: 'Nebraska', NV: 'Nevada', NH: 'New Hampshire', NJ: 'New Jersey', NM: 'New Mexico', NY: 'New York', NC: 'North Carolina', ND: 'North Dakota', OH: 'Ohio', OK: 'Oklahoma', OR: 'Oregon', PA: 'Pennsylvania', RI: 'Rhode Island', SC: 'South Carolina', SD: 'South Dakota', TN: 'Tennessee', TX: 'Texas', UT: 'Utah', VT: 'Vermont', VA: 'Virginia', WA: 'Washington', WV: 'West Virginia', WI: 'Wisconsin', WY: 'Wyoming'};
        var $el = $("#location-country");
        $el.data('oldval', $el.val());
        $el.change(function(){
            var $this = $(this);
            if(this.value=="US" && $this.data('oldval')!="US"){
                var str = '<select name="location-state" id="location-state">';
                orig_html = $("#location-state-div").html();
                orig_value = $("#location-state").val();
                for(var st in us_states){
                    if(st == state_value)
                        str += '<option value="'+st+'" selected="selected">'+us_states[st]+'</option>';
                    else
                        str += '<option value="'+st+'">'+us_states[st]+'</option>';
                }
                str += "</select>";
                $("#location-state-div").html(str);
                $this.data('oldval', $this.val());
            }
            else if($this.data('oldval')=="US" && $this.val()!="US"){
                state_value = $("#location-state").val();
                $("#location-state-div").html(orig_html);
                $("#location-state").val(orig_value);
                $this.data('oldval', $this.val());
            }
        });

    });


</script>




<div id="location-country-div">
    <select id="location-country" name="location_country">
    <option value=""></option> 
    <option value="US">United States</option> 
    <option value="United Kingdom">United Kingdom</option> 
    </select>
</div>



<div id="location-state-div">
    <input id="location-state" type="text" name="location_state" />
</div>