:Illanmaster

{{refimprove|date=August 2012}}

{{Use dmy dates|date=November 2021}}

{{Use Irish English|date=November 2021}}

{{Infobox islands

| name = Illanmaster

| image_name =

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| map = island of Ireland

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| native_name = Oileán Máistir

| native_name_link = Irish language

| nickname =

| location = Atlantic Ocean

| coordinates = {{coord|54|20|N|9|38|W|region:IE_type:isle|display=inline,title}}

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| country = Ireland

| country_admin_divisions_title = Province

| country_admin_divisions = Connacht

| country_admin_divisions_title_1 = County

| country_admin_divisions_1 = Mayo

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| population = 0

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Illanmaster or Illaunmaistir ({{Irish place name|Oileán Máistir}}) is an uninhabited steep rocky island rising to about 100m, lying just off the north coast of County Mayo, Ireland and {{convert|19|km|0|abbr=on}} west of Ballycastle. Grid ref: F 933 435.{{cite web | title=Illaunmaistir, Co. Mayo | work=BirdWatch Ireland | url=http://www.birdwatchireland.ie/Default.aspx?tabid=216 | accessdate=2008-06-27 | archive-url=https://web.archive.org/web/20080619051238/http://www.birdwatchireland.ie/Default.aspx?tabid=216 | archive-date=2008-06-19 | url-status=dead }} The island is separated from the mainland by a narrow sound.