I don't know that anyone could give you an answer to that - as far as I know it's traditional. On Mudcat, there's a Mr Bobby Bob (from Ellen Vannin) who has given a Conemara version of it that he found in Cas Amhrán compiled by Micheál Ó hEidhin - so it's not exclusively from Donegal. Here it is -

Curfá
Dilin ó deamhas, ó deamhas
Dilin ó deamhas ó dí;
Dilin ó deamhas, ó deamhas
Dilin ó deamhas ó dí.

Cuirfead mo rún chun suain
Cuirfead mo rún 'na luí;
Cuirfead mo rún chun suain go ciúin,
Le dilin ó deamhas ó dí.

Curfá

'S buachaill maith súiste, súist',
Is buachaill maith súist' é Páid;
Is buachaill maith súiste, súiste, súist',
'S cailín deas tuirn' i Cáit.

Curfá

Is buachaill aniar, aniar,
Is buachaill aniar an fear;
Is buachaill aniar, aniar, aniar,
'S is cailín ón sliabh an bhean.

Curfá

Caithimis suas is suas é,
Caithimis suas an páiste;
Caithimis suas is suas is suas,
'S tiocfaidh sé anuas amárach

Curfá