Irish Social Security

That can be complicated.  I want to refer this to another expert, @pk12_2

If there is a tax treaty with the other country, there are two ways to treat a government pension/social security plan.  

1. Follow the laws of the other country in paying income tax on the social security benefit in that country.  If you do that, then it is not taxable at all in the US and does not have to be reported on your US tax return.  (This is relying on the treaty.)

2.  If you choose not to follow the laws of the home country, then you report it as "miscellaneous/other taxable income" on your US tax return.

Obviously, what works best for you depends on the laws of your home country regarding paying tax on the social benefit. 

@Justinmcken , agreeing with the general comments  by my colleague @Opus 17 , I would like to add the following :

(a) generally  , i.e. for most treaty countries, govt. pension and payments from Social Security equivalents are taxable only by the country disbursing the payment.

(b) Ireland is an outlier in this :

     1. Article 18 of the treaty --

             (a) Subject to the provisions or Article 19 (Government Service) pensions and other similar remuneration derived and beneficially owned by a resident of a Contracting State in consideration of past employment shall be taxable only in that State; and b) notwithstanding the provisions of Article 19, payments made by a Contracting State under provisions of the social security or similar legislation of that State to a resident of the other Contracting State shall be taxable only in that other State

        2.   Technical Explanation further clarifies:

Subparagraph 1(b) The treatment of social security benefits is dealt with in subparagraph 1(b). This subparagraph provides that payments made by one of the Contracting States under the provisions of its social security or similar legislation to a resident of the other Contracting State will be taxable only in the other Contracting State. This subparagraph applies to social security beneficiaries whether they have contributed to the system as private sector or Government employees. The reference to “provisions of the social security” legislation is not restricted to old age pensions but refers to all sorts of social security benefits, including benefits granted in kind and payments made as compensation for work-related diseases or accidents. Paragraph 2 of the diplomatic notes explains that the phrase “similar legislation” is intended to refer to United States tier 1 Railroad Retirement benefits.

Thus the taxability is "residency" based.

Based on the above , my opinion is that your Irish Social Security payments are taxable ONLY by the US and not Ireland.

However, there is no mechanism for you to declare/recognize this income as "Social Security" and its taxability rules. So you are left with  treating this income as if it was private pension ( a-la 1099-R ) but with Unknown basis i.e. fully taxable amount.

Note that this treatment of Social Security equivalent is different  from other countries like Australia -- 

Article 18 ---

(2) Social Security payments and other public pensions paid by one of the Contracting States to an
individual who is a resident of the other Contracting State or a citizen of the United States shall be
taxable only in the first-mentioned State.

So that is where I stand.

Is there more one of us can do for you ?