1. Ireland.

Nuttall's Standard dictionary of the English language By Nuttall, P.Austin

• trein,
• irain,
• serian,
• ehrn,
• urin,
• virin,
• earing,
• reuin,
• vering,
• eting,
• orfin,
• hearin,
• egine,
• aprin,
• eaing,
• arsin,
• erging,
• cerian,
• trin,
• eri

• grin,
• Eryn,
• erion,
• Erna,
• erwinia,
• Erma,
• errhine,
• rein,
• Ernie,
• ern,
• Erwin,
• erne,
• Erinn,
• erie.

The plural form of the word "Erin" is "Erins".

The singular form of the word "Erin" is still "Erin". It is a name and does not have a different singular form.