The effects of the IDA's new policy to encourage potential investors to locate in the Objective 1 area will not be felt immediately, according the IDA's regional manger in the north-west, Mr Joe McHugh.
He said there had been a "steady flow" of potential investors into counties Sligo, Leitrim and Donegal this year although there has only been one start-up, by American health insurers PacifiCare, which is to employ 160 people in Letterkenny.
"Switching the flow of business to target locations isn't something that can happen overnight," Mr McHugh said.
The IDA recently suffered a setback in efforts to find alternative industries for the former Fruit of the Loom plants when a German engineering firm withdrew from negotiations about locating in the Milford factory.
"We had been reasonably confident that they were going to go ahead, but then they told us they had decided to buy an existing company in Spain instead. It was a blow because we had put a lot of work into it."
Before progress could be made on selling the locations, it was necessary to have quality facilities available and a number of buildings were now under construction, he said.
A 25,000 sq ft multi-purpose factory was completed this week at the Finisklin Industrial Estate in Sligo and work has also started on a large advance office space in the same estate. An advance factory is to be built in Carrick-on-Shannon and work has also started on two new buildings in Letterkenny, similar to those in Sligo.
The Fruit of the Loom plants are much larger than the new buildings at about 60,000 sq ft. "The more options we have to offer clients the better," Mr McHugh said.
The IDA is in discussion with at least six companies at any one time, but there was increasing pressure from places such as Scotland, he said. Marketing the new factory in Sligo was a priority.
It was also negotiating with companies about the Malin and Raphoe Fruit of the Loom plants and efforts would now have to be refocused on the Milford plant.