US church member sat in yard casually with coffee (6-3,5)

'us church member' is the definition.
(as in The Church of Latter-day Saints)

'sat in yard casually with coffee' is the wordplay.
'casually' indicates anagramming the letters (I've seen this in other clues).
'with' says to put letters next to each other.
'coffee' becomes 'latte' (I've seen this before).
'sat'+'in'+'yard'='satinyard'
'satinyard' anagrammed gives 'rdaysaint'.
'rdaysaint' after 'latte' is 'LATTER-DAY SAINT'.