1 John, 2 John and 3 John
We do not know when these letters where written. Their content indicates a later date. With the latest date of John's death set at A.D. 98, it appears likely that these letters were written in the A.D. 90's.
Encountering the New Testament, Walter A. Elwell / Robert W. Yarbrough, 1998, Baker Books, page 368