O.E. æt, common P.Gmc. (cf. O.N., Goth. at, O.Fris. et, O.H.G. az), from PIE *ad- "to, near, at" (cf. L. ad "to, toward" Skt. adhi "near"). Lost in Ger. and Du., which use their equivalent of to; in Scandinavian, however, to has been lost and at fills its place. At-home (n.) "reception of visitors"
is from 1745; baseball at-bat "player's turn at the plate" is from 1941. The colloquial use of at after where ("where it's at") is attested from 1859. In choosing between at church, in church, etc. at is properly distinguished from in or on by involving some practical connection; a worshipper is at church; a tourist is in the church. At last is recorded from late 13c.; adv. phrase at least was in use by 1775. At in M.E. was used freely with prepositions (e.g. at after, which is in Shakespeare), but this has faded with the exception of at about, which was used in modern times by Trollope, Virginia Woolfe, D.H. Lawrence, and Evelyn Waugh, but nonetheless is regarded as a sign of incompetent writing by my copy editor bosses.