| John George I | |
| Succession: | Duke of Saxe-Marksuhl |
| Reign: | 1662–1686 |
| Predecessor: | New Creation |
| Successor: | Johann Georg II |
| Succession1: | Duke of Saxe-Eisenach |
| Reign1: | 1671–1686 |
| Predecessor1: | William August |
| Successor1: | Johann Georg II |
| Spouse: | Johannetta of Sayn-Wittgenstein |
| Issue: | Eleonore Erdmuthe Luise, Margravine of Brandenburg-Ansbach and Electress of Saxony Frederick August, Hereditary Duke of Saxe-Eisenach Johann Georg II, Duke of Saxe-Eisenach John William III, Duke of Saxe-Eisenach Fredericka Elisabeth, Duchess of Saxe-Weissenfels |
| House: | Wettin |
| Father: | Wilhelm, Duke of Saxe-Weimar |
| Mother: | Eleonore Dorothea of Anhalt-Dessau |
| Birth Date: | 12 July 1634 |
| Birth Place: | Weimar |
| Death Place: | Eckhartshausen, Marksuhl |
| Religion: | Lutheran |
Johann Georg I, Duke of Saxe-Eisenach (Weimar, 12 July 1634 - hunting accident, Eckhartshausen, Marksuhl, 19 September 1686) was the fifth but third surviving son of Wilhelm, Duke of Saxe-Weimar and Eleonore Dorothea of Anhalt-Dessau.
After the death of his father (1662), his older brother Johann Ernst II inherited Weimar, and his second brother Adolf Wilhelm received Eisenach. Johann Georg received an income from the new duchy of Saxe-Eisenach and took his residence in the small town of Marksuhl.
In 1668 his brother Adolf Wilhelm died. His fifth and only surviving son, Wilhelm August, was born eight days after his father's death and became duke from the moment of his birth; Johann George became the regent of the duchy and also the guardian of the new duke. Wilhelm August died in 1671 at only two years of age, and Johann Georg inherited the duchy.
The next year (1672) the death without heirs of the Duke Frederick Wilhelm III of Saxe-Altenburg forced a new treaty of division of the family lands between Johann Georg, his surviving brothers and his cousin. Johann Georg was confirmed in his possession of Eisenach and took some towns, and his younger brother, Bernhard, inherited Jena.
In the spring of 1672, when Johann Georg officially moved his residence from Marksuhl to Eisenach, the occasion was marked by a special Easter church service with music composed by Ambrosius Bach.[1] His move reestablished Eisenach's status as the capital of the principality.
Johann Georg thus became the founder of the most recent line of the dukes of Saxe-Eisenach, who became extinct in 1741. He was ruler in 1685 when Johann Sebastian Bach was born in the duchy.
In Wallau on 29 May 1661, Johann Georg married the Countess Johannetta of Sayn-Wittgenstein, heiress of Sayn-Altenkirchen. They had eight children:
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