William I of Hesse (German: Wilhelm) (4 July 1466 – 8 February 1515) was the Landgrave of Hesse (Lower Hesse) from 1471 to 1493.
His parents were Louis the Frank (1438–1471) and Mechthild, daughter of Count Louis I of Württemberg.
On 17 February 1488 in Münden, he married Anna of Brunswick-Wolfenbüttel c.
1460 - Worms 16 May 1520], daughter of William II, Duke of Brunswick-Wolfenbüttel and Elisabeth, Countess of Stolberg, with whom he had five daughters:
Mathilda, born in 1489 but died young.
Mathilda (born 1490; died 6 May 1558), married in Korbach on 19 May 1527 Konrad, Count of Tecklenburg (born 1493; died 16 August 1557)
Anna (born 1491; died 1513), a nun
Katherine (died 1525), married in 1511 Adam Count von Beichlingen (died Krayenberg 14 July 1538)
Elisabeth [10 September 1503 - Lauingen 4 January 1563], first married in Meisenheim on 16 October 1525 to Louis II, Count Palatine of Zweibrücken (born 1502; died 1532), later married on 9 January 1541 George, Count Palatine of Simmern (born 1518; died 1569).After a pilgrimage to the Holy Land in 1491 where he was dubbed a Knight of the Holy Sepulchre, he probably contracted syphilis.
He abdicated in favor of his brother William II on 3 June 1493, and spent his life in Spangenberg.