Getting the counties of Finland correct is a bit of a hell, seeing that both when Finland was governed from Stockholm, and when the Finns finally got to be in charge of their own affairs, administrators seems to have had an itch to reform local government boundaries every twenty-five years or so. The other Max informs me that this has to do with the uneven population growth and other changes in demography that Finland has experiences over the centuries, which would seem to imply that the reforms have, at least for the most part, been sensible and pragmatic.
During the slightly more than one hundred years that Finland was a Grand Duchy in the Russian Empire (curious isn't it by the way how Великий Князь translates into
Grand Duke, while Князь translates to
Prince, and the Russian word for
Duke without any grandeur added to it is Герцог, which evidently is taken from the German
Herzog; one would almost suspect that the English words for titles in the Russian peerage can be traced back to a shitty or inconsistent translator operating at some point in history), the government of the Tsar, infamous for their reluctance to do any administrative reform whatsoever, Finland's internal borders remained relatively static, and there exists a wealth of maps from that era.
I've decided to go with the county borders of Finland as they existed around 1800, which is possible to reconstruct from a little map archeaology, and only add changes if I can come up with a good explanation for it. As such it seems reasonable that Tavastehus and Nyland county is separated as per OTL into Tavastehus County and Nyland county, for instance. This gives pretty much the borders that
@Ares96 himself came up with, and as far as I can see, I only am going to have to change two or maybe three of the constituencies that he so kindly worked out for me this past autumn.
And here is as of yet the only county I've been able to trace out so far, Åbo/Turku: