In the year of our Lord.
The A.D. should precede the date and never be used with in
, since that would be superfluous
. Nor should the A.D. be used when speaking of a century
Wrong: He died in 1865 A.D.
Right: He died A.D. 1865.
Wrong: We live in the 20th century A.D.
Right: We live in the 20th century of the Christian Era.
From the American College Encyclopedic Dictionary, vol. II (1952)