John I, Count of Henneberg-Schleusingen

John I of Henneberg-Schleusingen (1289 – 2 May 1359) was a younger son of Berthold VII the Wise. Years in his father's retinue gave him court contacts, and in 1334 he negotiated the release of Prince Otto, captured after the battle of Viborg, though on terms so heavy that the Danes resented him.

When his brother Henry VIII died in 1347 leaving only daughters, John inherited the reduced northern part of the county, which left him weak against the bishopric of Würzburg, the old Henneberg rival. In 1348 he took the Würzburg burgraviate from Bishop Albert II as a fief, together with the hereditary marshal's office.

In 1349 he married Elisabeth of Leuchtenberg, and in 1356 Charles IV named him imperial councillor at the Nuremberg Diet. Debts and his own extravagance forced him to pawn castles and towns throughout his reign.