From this page you can lookup a Location Code for UK & Ireland counties, states and provinces in the US, Canada, Australia & New Zealand. You can also search for a Country code as well as lookup the Code for a particular county or state.

The codes are either 2 or 3 characters only.
The Search by County/State only needs the first couple of letters of the Country name to perform the search. Note: This list is not exhaustive - more codes can be added on request.

You can also browse the full set of Codes HERE