The G8 summit cost around £75m in policing and security costs - with Northern Ireland footing £15 million of the bill.
Stormont also forked out a further £5 million to improve roads and boost publicity - bringing Northern Ireland's costs to £20 million.
Approximately 8,000 police officers, many drafted in from the mainland, were on duty during the two-day gathering of world leaders in Co Fermanagh last month.
A huge steel barrier costing more than £4m was erected to cut off the small island on which the Lough Erne hotel sits, and every road surrounding the exclusive resort, including single-lane farm tracks, were shut to all but a handful of local residents.
Stormont Finance Minister Sammy Wilson told the Assembly: "The most important thing is that we successfully delivered a safe and secure event and for that I give my sincere thanks to the PSNI."
Only two arrests were made as protests against figures like US President Barack Obama and his Russian counterpart Vladimir Putin stayed peaceful. A wire fence near the Lough Erne resort was breached for a short time but the demonstration did not turn violent.
Millions were spent on temporary custody facilities at a former British Army barracks in Omagh and on training officers in handling disorder. But with no sign of dissident republican trouble or loyalist disorder, and with the number of anti-capitalist protesters relatively small, masses of officers had little to do.
The UK Government picked up £60 million of the cost and the rest of the policing bill was paid for by Stormont's Department of Justice, Mr Wilson said, adding that the total policing and security cost amounted to around £75 million. Another £5.1 million was spent on road improvements near the venue, a publicity campaign to maximise the economic benefits from the event, and money for ambulance and fire services.
The minister added: "We must recognise that the G8 event has the potential to generate huge economic benefits for Northern Ireland. That is why the event will be followed by an investment conference in the autumn.
"Of course, we will not know the full economic benefits for years to come."