Workers at the Hospira plant were numbed by the announcement that the plant would close.
The news was broken to about 300 employees when they were summoned to the canteen for a meeting at 10am yesterday.
Most of the workers, who earn an average take-home wage of €360 a week, were caught unawares.
A few thought something might have gone wrong with an order and they were to be given a lecture.
Mother of two Mary Thomas, from the village of Frosses said: "There was some expectation that there might be a few redundancies. But at no time did anybody, even in management, suspect there would be total closure."
Ms Thomas (52), an employee of 16 years said: "We're all numb. I know that at my age there won't be any other work in the area for me. But I'm lucky. My children are reared and my husband still has his job.
"There are hundreds in their 20s and 30s, including couples who met in the plant, who kept saying 'what are we going to do?'
"What other employment is there in the northwest? There is nothing. It was such a wonderful place to work. People really felt their jobs here would last forever."
Around half the employees were women on four-hour daily shifts with take-home pay of around €180 a week. They regarded working conditions as ideal for rearing families.
Margaret Breslin, from Inver, a mother of four children aged from nine months to 12 years, said: "I'm not a happy chick. Everybody is in shock, just devastated. I was gobsmacked.
"We don't know what we're going to do. Where in Donegal are the jobs nowadays? There just isn't a bright side to this at all."
Ms Breslin, who is three years at the plant added: "There seemed to be plenty of work for the plant. The whole place, including the car park, was done up only recently. The signs were for long employment rather than this."
Another mother of four, Fiona Duncan, from Ballydevitt, Donegal Town, is 14 years at Hospira. She said: "I have been told I am out of work in 18 months. I don't know what I'm going to do. There's not much other work around."
More than 420 employees are members of Siptu. Donegal branch secretary Seán Reilly said: "There wasn't a hint. This was totally unexpected. We were talking to the company only six weeks ago and things seemed to be going very well. This is a bolt out of the blue."
He said he would be seeking the best possible redundancy package for his members.
He added: "These losses are the latest in an extremely long line of job losses in Co Donegal in recent years."