https://en.wikipedia.org/wiki/The_Twelfth
It’s not what it once was. Reduces in scale with each year as there are fewer radicals left to cause trouble. However, there are certain pockets of the country that take it way too seriously but these are unlikely to be places you’ll visit anyway.
I’ll disagree with the other person though. Definitely visit in July to take advantage of the weather. Go see the Giants Causeway it is a stunning sight.
Source: NI born and bred.
Not sure where you were but not my experience at all. I’ve never seen anything close for days let alone weeks around the twelfth.