Agnes von Mansfeld-Eisleben (1551–1637) was Countess of Mansfeld and the daughter of Johann (Hans) Georg I, of Mansfeld Eisleben. She converted Gebhard, Seneschal of Waldburg, the Prince-Elector of Electorate of Cologne and archbishop of the Diocese of Cologne to the Protestant faith, leading to the Cologne War (1583–1588).