Code:
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<title>Any Title</title>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<script type="text/javascript">
var zipCodes =[];
zipCodes["counties"] = ["Summit","Jefferson"];
zipCodes["Summit"] = ["44101","44107","44116","44135","44147"];
zipCodes["Jefferson"] = ["44221","44266","44270"];
function fillSelect(isValue,isNext){
isNext.length = 1;
var curr = zipCodes[isValue];
for (each in curr)
{
var nOption = document.createElement('option');
var isData = document.createTextNode(curr[each]);
if (each=="0"&&isValue=="Jefferson") {
nOption.selected="selected";
}
nOption.setAttribute('value',curr[each]);
nOption.appendChild(isData);
isNext.appendChild(nOption);
}
}
function init(){
fillSelect('counties',document.forms[0]['county']);
}
onload=init;
</script>
<style type="text/css">
body {background-color:#eae3c6;margin-top:60px}
form {width:350px;margin:auto}
fieldset {background-color:#f0fff0;border:1px solid #87ceeb}
legend {font-family:times;font-size:14pt;color:#00008b;background-color:#87ceeb;padding-left:3px;padding-right:3px;margin-bottom:5px}
label {font-family:times;font-size:12pt;color:#00008B;padding:5px}
select {font-family:times;font-size:10pt;margin:10px}
.submitBtn {display:block;margin-left:auto;margin-right:auto;margin-top:5px;margin-bottom:5px}
</style>
</head>
<body>
<form method="post" action="">
<fieldset>
<legend>Zip Code</legend>
<select name='county' onchange="fillSelect(this.value,this.form['zipCode'])">
<option selected>Select Your County</option>
</select>
<select name='zipCode'>
<option selected>Select Your Zip Code</option>
</select>
<input type='submit' name='submit' value="Submit" class='submitBtn'>
</fieldset>
</form>
</body>
</html>
did you want jefferson selected first too? or did you mean select jefferson and have a certain zipcode?
here is the specific code that i added
Code:
if (each=="0"&&isValue=="Jefferson") {
nOption.selected="selected";
Before you post, read our: 
