María de Salinas, Baroness Willoughby de Eresby (ca. 1490 – 1539) was a noblewoman from Spain. She served as confidante and lady-in-waiting to Catherine of Aragon, Queen of England.
Maria was the daughter of Martín de Salinas (d. 1503), and Josefa González de Salas, who were members of the royal household in Castile, and probably related to the royal family. She had a younger sister, Ines, born in 1491, who died sometime after she did.
The exact date that Maria became a maid-of-honour to Catherine of Aragon is unknown, but is thought to have been in 1501. Maria remained unmarried until 5 June 1516, when she married the English nobleman William Willoughby, 11th Baron Willoughby de Eresby, and they had one child, Catherine Willoughby, who succeeded to her father's barony and later became Duchess of Suffolk by marriage. Grimsthorpe Castle was granted by Henry VIII to the de Eresby family on the occasion of Maria's marriage. Henry esteemed Maria so much that in 1522 he named a ship 'HMS Mary Willoughby' in her honour.
In 1511 Maria became the godmother to Mary Brandon, the daughter of Charles Brandon, 1st Duke of Suffolk and his second wife Anne Browne. Lord Willoughby died in 1526; the Duke of Suffolk made Maria's daughter, Catherine, his ward shortly thereafter, marrying her as his fourth wife in 1533. Maria spent several years fighting her brother-in-law, Sir Christopher Willoughby, for control of the Willoughby estates on behalf of her daughter.
Maria was a devoted friend to Catherine of Aragon. In August 1532, shortly before Catherine's marriage to Henry was annulled, she was ordered to leave Catherine's household and not to make any attempt to communicate with her. In September 1534, when Catherine's health deteriorated, Maria begged permission to visit her but was denied. On 5 January 1536 she forced her way into Kimbolton Castle to see Catherine, having again been refused permission to visit. Catherine died in her arms two days later.