De or het ierland?

The correct Dutch article is:

het ierland

How to use ierland

the ierlandhet ierland
this ierlanddit ierland
that ierlanddat ierland
our ierlandons ierland
your ierlandjouw ierland
every ierlandelk ierland
which ierland?welk ierland?
a big ierland / the big ierlandeen groot ierland, het grote ierland

Dutch words ending in ierland

noord-ierland

In compound words, the last part decides the article. See the rule