The Schengen Agreement is a treaty that was signed in 1985 between several European countries to eliminate border checks and allow for free movement of people and goods within the agreement area. While Southern Ireland is a part of the European Union, it is not a part of the Schengen Area Agreement.

The Republic of Ireland, which encompasses both Northern and Southern Ireland, is a member state of the European Union. However, the country opted out of the Schengen Agreement during its formation. As a result, Southern Ireland remains outside of the Schengen Area, which includes 26 European countries, most of which are members of the European Union.

The decision to opt-out of the Schengen Agreement was made to maintain the integrity of Ireland`s common travel area with the United Kingdom. The common travel area allows for the free movement of people and goods between the two countries, which would have been disrupted if Ireland had joined the Schengen Area.

It is important to note that while Southern Ireland is not a part of the Schengen Agreement, travelers may still be subject to passport control when entering or leaving the country. This is because the Republic of Ireland maintains its own distinct immigration policies and controls.

In conclusion, Southern Ireland is not a part of the Schengen Agreement, which allows for free movement of people and goods within the agreement area. The decision to opt-out of the treaty was made to maintain the integrity of Ireland`s common travel area with the United Kingdom. Travelers to Ireland may still be subject to passport control when entering or leaving the country, as the country maintains its own distinct immigration policies and controls.