Sayn-Wittgenstein-Sayn-Altenkirchen (sometimes called Sayn-Altenkirchen) was a German county located in what is now Rhineland-Palatinate, near the river Sieg.

When Count William III of Sayn-Wittgenstein-Sayn died in 1623 without clear heirs, the Archbishop of Cologne occupied the vacant County until the succession was settled.

[citation needed] It was settled by treaty in 1648, when the County was given jointly to Princesses Ernestine and Johanette, two sisters who were granddaughters of Count William, and their mother Dowager Countess Louise Juliane made regent.

William Henry died childless and Sayn-Altenkirchen was inherited by Charles, Margrave of Brandenburg-Ansbach, Johanette's great-grandson.

Queen Caroline, wife of George II of Great Britain, was co-heiress to this County, but she never inherited it and her grandson George III was compensated for his loss of inheritance to it.