I came across this breakdown on a site about the Icelandic language.
It is based on the original sources. I am sharing this information
mostly because it pertains to the origins of Old Icelandic. Enjoy.

Norðmenn (Norwegians) 85%

Frá Mið-Vestur-Noregi 39%
Frá Rogalandi og Ögðum 12%
Frá Þrændal. og nágr. 15%
Frá Norður- og A-Noregi 19%

Frá Bretlandi, flestir norrænir, aðrir keltar 12%
(from Britain, mostly Norse, others Celtic)

Frá Svíþjóð o. fl. löndum, flestir norrænir 3%
(from Sweden and other lands, mostly Norse)

Alls (total) 100%

Now let us consider how far modern linguistics has advanced. Even if
we had no information about early Icelanders except some remains of
their language, we would still be able to piece together a breakdown
similar to the one above - the language clearly shows its origin.

Regards,
Konrad.