Hid a horse around part of US (5)
I believe the answer is:
idaho
'part of us' is the definition.
(I've seen this before)
'hid a horse around' is the wordplay.
'around' indicates the answer is hidden within the clue.
'IDAHO' is hidden within 'hid a horse'.
(Other definitions for idaho that I've seen before include "Northern US state" , "My Own Private -- (1991 film)" , "Union member?" , "US location" , "The Gem State, known for its potatoes" .)