Division of an English county is a square (7)

I believe the answer is:

hundred

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'division of an english county' is the definition.
'hundred' can be an answer for 'county' (thesaurus). I'm not sure about the 'division of an english' bit.

I cannot understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for hundred that I've seen before include "See 19" , "so many others" , "Subdivision of shire; ton" , "cricketing achievement" , "Old subdivision of a shire or county" .)

I've seen this clue in The Times.

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