Terrible army, one coming down -- I'm in a state (10)

I believe the answer is:

marylander

'i'm in a state' is the definition.
(someone from Maryland)

'terrible army one coming down' is the wordplay.
'terrible' is an anagram indicator.
'one coming down' becomes 'lander' (come down can mean to land).
'army' with letters rearranged gives 'mary'.
'mary'+'lander'='MARYLANDER'

I've seen this clue in The Telegraph.

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