In the fourth millennium BC, the first farmers arrived in Ireland. They buried their dead in large stone-built chambered tombs known as megalithic tombs. There are about 160 tombs in County Mayo.

The Céide Fields are the oldest known field systems in the world, over five and a half millennia old.

St. Patrick came to County Mayo, where he spent forty days and nights  fasting and praying on the summit of Croagh Patrick .In the 6th century hundreds of monastic settlements were established in Mayo.

In the 9th century when the Vikings invaded, monasteries in Mayo built round towers for protection. Many monasteries were destroyed.

After the Norman invasion in 1169, Mayo came under their control in 1235. In the 16th century Gráinne Ní Mháille, Grace O'Malley was lord of the Ó Máille dynasty. She was known as the "sea-Queen".

Charles C Boycott was an English land agent who became infamous after he was ignored and ostracized - boycotted - by the Mayo Irish community.

On the 21st August, 1879 fifteen people from the village of Knock in Co. Mayo, claimed to have witnessed an Apparition of Our Lady

Michael Davitt was the leader of the rural Irish agricultural people during the land campaign in the 19th century.

Frank Stagg and Michael Gaughan from Mayo died on hunger strikes in prison in England in the 1970s.

Famous people from Mayo include: Gráinne Ní Mháille, Mary Robinson, Ernie O'Malley, Michael Gaughan, Charles Haughey, Enda Kenny, Michael Davitt, Sean MacBride, William O'Dwyer, Paul O'Dwyer, P.J. Ruttledge, Sally Rooney, Frank Stagg, Louis Walsh.