Based off the names, some may believe that Northern Ireland is just a northern part of Ireland, but in fact, Northern Ireland and Ireland are two separate countries. One of the differences between the two is that Ireland is independent, while Northern Ireland is apart of Great Britain. Another difference between them is the language they speak. In Northern Ireland, English is spoken. In Ireland, English is also spoken, but they also have people that speak Irish and Gaelic. Along with the differences in language, they also have a different size population. Ireland is larger with 4 million people, while Northern Ireland has one million people.
The partitioning of Ireland happened in the early 20th century. One main difference between the two is they use different types of metric systems. You will see in Ireland that they use kilometers per hour, but in Northern Ireland, they use miles per hour. Do remember that they have some other differences aside from this. In Ireland, they use Polish more as their main language instead of Irish.
In fact, more people there will probably understand Polish more instead of Irish. In Northern Ireland, English is considered to be the main language. One similarity between the two is Christianity is considered to be the most popular religion although there are other religions that are being followed by people who are living in both areas.