In
Altenburg on 7 January 1593, Johann married
Dorothea Maria of Anhalt (2 July 1574 - 18 July 1617). They had twelve children in just twelve years: •
John Ernest I, Duke of Saxe-Weimar (b. Altenburg, 21 February 1594 – d. Sankt Martin, Hungary, 6 December 1626). • Christian William (b. and d. Altenburg, 6 April 1595) died at birth. •
Frederick (b. Altenburg, 1 March 1596 – killed in battle, Fleurus, Belgium, 29 August 1622). • John (b. Weimar, 31 March 1597 – d. Weimar, 6 October 1604), died in childhood. •
William, Duke of Saxe-Weimar (b. Altenburg, 11 April 1598 – d. Weimar, 17 May 1662). • Stillborn son (Altenburg, 11 April 1598), twin of William. •
Albert IV, Duke of Saxe-Eisenach (b. Altenburg, 27 July 1599 – d. Eisenach, 20 December 1644). •
John Frederick (b. Altenburg, 19 September 1600 – d. Weimar, 17 October 1628). •
Ernest I, Duke of Saxe-Gotha (b. Altenburg, 25 December 1601 – d.
Schloss Friedenstein, Gotha, 26 March 1675). • Frederick William (b. Weimar, 7 February 1603 – d. Georgenthal, 16 August 1619), died unmarried and without issue. •
Bernhard (b. Weimar, 6 August 1604 – d. Neuenburg, 18 July 1639), Count of Franken (1633). • Johanna (b. posthumously, Weimar, 14 April 1606 – d. Weimar, 3 July 1609), died in childhood. ==Ancestry==