Lady Henrietta Augusta Lloyd-Mostyn (née Nevill; 18 June 1830 – 25 January 1912) was a philanthropist and artist who contributed to the development of the Welsh town of Llandudno. She was born at Birling Manor near Maidstone, Kent. Her parents were William Nevill, 4th Earl of Abergavenny and Caroline Leeke. Her sisters, Caroline Emily Nevill and Isabel Nevill, were also photographers. On 19 July 1855 Augusta Nevill married Thomas Lloyd-Mostyn. They had two sons, Llewelyn Neville Vaughan Lloyd-Mostyn and Harry Richard Lloyd-Mostyn. They lived at Gloddaeth Hall.
Lady Augusta Mostyn commissioned All Saints Church, Deganwy from the architect John Douglas as a memorial to her parents. She commissioned the Mostyn Art Gallery in Llandudno, the precursor of the current MOSTYN gallery, as a headquarters for the Gwynedd Ladies' Arts Society. This is thought to have been the first art gallery dedicated to exhibiting work by female artists in the world.