I checked your account again, and yes County is available in those sections. I was able to make a segment with "county" being a custom field selection under contact details. I was able to export your contacts with custom field info checked on, and county was included.
Keep in mind only a single one of your contacts actually has any data entered for the "county" custom field, so you may not be noticing the custom field's inclusion in certain elements because it's blank for your other contacts.
You can go into your account right now and check out the "county test" segment I made, as well as go to your import/export activity page to download the CSV file I generated where county is clearly visible and available as an exportable field. See my earlier comment if you need guidance on where to find these functionalities in your account.
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