County Mayo on Wikipedia.

Achill Sound (on Achill Island), Sisters of Mercy (R.C.). © Bill Henderson.

Ballina, Cathedral of St. Muredach (R.C.1827). Interior view. Link. St. Michael. All © John Balaam (2016).
Ballindine, St. Joseph (R.C., 1884). M 368 692. © Gerard Close (2017). Link.
Ballintubber (also Ballintober), the Abbey (R.C.). © Len Brankin. Link1. Link2.
Bohola, Church of the Immaculate Conception and St. Joseph Bohola (R.C.). © Bill Henderson.

Bunnacurry, St. Joseph. (R.C.). © Bill Henderson.

Charlestown, St. James (R.C.). G 477 018. © Gerard Close (2016). Link.
Claremorris, St. Colman (R.C.). Interior view. M 341 752. Both © Joseph Cantwell (2011). Another view, © Gerard Close (2017). The former CoI St. John was built in 1828, and was closed in 1963. It now serves as a library. M 341 752. © Gerard Close (2017).
Cong.
Crossmolina, St. Mary (CoI). © Bill Henderson.

Finney, Immaculate Conception (R.C.). © Len Brankin.
Foxford, St. Mary & St. Michael (R.C.). Church of Ireland. © Bill Henderson.

Glencorrib, Church of the Immaculate Conception (R.C.). © Bill Henderson.

Glenhest, St. Joseph. (R.C.). © Bill Henderson.

Kildonnet (on Achill Island), ruins of the old R.C. church. © Bill Henderson.
Kilkelly, St. Celsus (1960, R.C.). M 441 916. © Gerard Close (2016). Link.
Kiltamagh, Church of the Holy Family (1888, R.C.). M 341 892. © Bill Henderson. Another view, © Gerard Close (2016).
Knock, the Roman Catholic Basilica. © Bill Henderson. Another view, © Gerard Close (2014). St. Joseph at the Shrine (R.C.) (© Bill Henderson) - this is the apparition chapel, which encloses the rear wall of the original church, © Gerard Close (2014). Just visible behind St. Joseph is the old church still in use. © Graeme Harvey. Another view, © Gerard Close (2014). Blessed Sacrament Chapel, © Gerard Close (2014). Chapel of Reconciliation, © Gerard Close (2014).Map reference (for all) is M 394 827.

Louisburg, St. Patrick (R.C.). © Bill Henderson.

Mulranny, Catholic Church. © Bill Henderson.

Newport, St. Patrick (R.C.). © Bill Henderson.

Partry, St. Mary (R.C.). © Len Brankin.
Pollagh, St. Patrick (R.C.). © Bill Henderson.

Shanvaghera, St Anne (R.C.). © Graeme Harvey.

Straide, Catholic Church. © Bill Henderson.

Swinford, Church of Our Lady (R.C.). © Bill Henderson.

Turlough, Church of Ireland. © Bill Henderson.

Westport, St. Mary (R.C.). Holy Trinity (CoI). © Bill Henderson.