With the exception of the University of Limerick, undergraduate degrees take three years to complete in Ireland (Limerick has a four-year system similar to the US). Students specialize in a field and pursue all of their courses in only a couple of departments. For example, at Dublin City University, a three-year institution, it is safe to say that first year courses will be equivalent to sophomore level coursework in the US.
Don’t be surprised if learning at an Irish university is quite different from what you’re used to in the US. More responsibility is placed upon you for learning the course material. During the school week, you’ll attend large lectures followed by more intimate tutorials and labs where the information is studied in detail. The expectation is that you will read and research without much formal structure (no weekly assignments or exams) and that you will spend much of your time independently preparing outside of the classroom. The academic calendar in Ireland has a fall semester that starts later than traditional US universities and extends into January and the spring semester starts shortly after and runs until early June.