One hermit seen wandering in county no longer (9)

I believe the answer is:

merioneth

'county no longer' is the definition.
(historic county of Wales)

'one hermit seen wandering in' is the wordplay.
'seen wandering' is an anagram indicator (I've seen this in other clues).
'in' indicates putting letters inside.
'hermit' anagrammed gives 'merith'.
'one' placed inside 'merith' is 'MERIONETH'.

(Another definition for merioneth that I've seen is " historic Welsh county".)

I've seen this clue in The Telegraph.

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