Upvote:4
Irish citizens typically qualify for the Visa Waiver Program (VWP) so don't require a Visa to enter the US. Instead you will need to get an ESTA before you travel, even for the land border.
There are no forms to fill out at the border anymore, everything is electronic. However you will still need a I-94 when you enter the US.
It is recommended you apply for an I-94 (for VWP and for Visa travelers) before you travel using the CBP One app (can also be done on the CBP I-94 website). Once you have paid for the I-94 on the app you must travel within 7 days to use it otherwise it will expire. You will still have photo and fingerprints taken at the border when you enter the country.
Obtaining the I-94 via the CBP One app is currently only possible for people entering the US via a land port of entry. Those flying in or entering by ship will continue to be processed by the CBP officer at immigration.
Upvote:6
I don't know if they still require to fill paper forms for land entries, but if they do - only people using VWP (Visa Waiver Program) should fill I-94W (the green one), people seeking admission on any status other than WVP should fill I-94 (the white one).
ESTA is required for seeking admission under VWP, so someone who for whatever reason doesn't have ESTA - they will be denied entry if they don't have a visa.