HÄGGSTRÖM, Grete and son Jacob; bef 1801 -> Nordland, Norway

[Diana Austring]

I've just found my first Swedish ancestors!  NOW, I'd like to find out where in Sweden they came from and when!
 
59yo Grete HÄGGSTRÖM (born c1742) and her 19yo (probably illegitimate, since she was listed as single) son Jacob HÄGGSTRÖM (born c1781) were at Kvitnes gård in (Vesterålen, Nordland, Norway) where Grete worked as a maid in 1801. I would LOVE to find out where in Sweden she came from, who her family was and whether Jacob was born there or in Norway.  
 
Of course, it would also be fantastic to find out who Jacob's father was, but I'm not holding my breath for THAT one!
 
Any clues as to how to search effectively in Sweden would be GREATLY appreciated!