Definition of where someone is at in US English:

where someone is at

phrase

informal
  • Someone's true or fundamental nature or character.

    ‘I think we've got enough information to have an idea of where he's at’
    • ‘This is Rethel's most precise determination of who and where he is at that moment.’
    • ‘The first bit is exactly where my thinking is at.’
    • ‘So that's where my head is at these days.’