It is a small place for the big hitters. The Prime Minister, his two immediate predecessors and the Chancellor have all campaigned in Northern Ireland.
There has been much debate about whether or not the soft Irish border would have to be hardened but the truth is no one knows.
It would not be a decision for the UK alone but also for Ireland and the rest of the EU for they share the border.
The armoured police checkpoints and customs posts are long gone but Ireland has been exploring the cost of having to re-instate at least some controls.
Until now, the Common Travel Area – an informal agreement – between the two countries has allowed free movement of people but produce is another issue.
It is simply not possible to predict what kind of trade relationship would be negotiated between the neighbours in the event of a UK exit.
Bilateral trade between them tops a staggering £1bn per week. Thirty percent of Ireland’s imports come from the UK – food, soft drinks, fashion and footwear.
The UK exports more goods to Ireland than to China, India and Brazil combined. The London-Dublin air route is the second busiest in the world.
With the Economic and Social Research Institute predicting a fall of 20% in bilateral trade, Ireland’s Prime Minister has expressed serious concern about the economy.
The east-west relationship is one thing, the north-south relationship another. Campaigners from Leave and Remain differ enormously on the potential impact on the peace process.
If Northern Ireland votes to remain but the UK votes to leave, the result of the referendum will raise the question of Northern Ireland’s sovereignty.
Sinn Fein will demand a poll on reunification – on Northern Ireland leaving the UK – quicker than the SNP will demand another referendum on Scottish independence.
EU funds, released to copper-fasten peace, would be gone too. Between 2007 and 2013, Northern Ireland received more than £2.4bn and has been promised more.
With 500,000 Irish people living in Britain and 300,000 British people living in the Republic of Ireland, the potential implications of a Brexit are significant.
Preserving the relationship between the UK and Ireland, who both joined the EU on the same day in 1973, will have to be a priority.