So its a made up city on one of the Great Lakes, Quietvalerie and I had a lot of discussion on this and I even have a rough timeline of the city's history and a mock sketch of the city layout.
So... What can I say?
Penrith is roughly based on a mix of Buffalo, Detroit and Chicago. Like these cities it is located on the shore of one of the Great Lakes, in Penrith's case it is on the eastern shore with the lake on the city's western side. Penrith was founded pre-Revolutionary War and was a Port Town used by ships transporting the products of logging, mining and hunting pelts before they joined the overland route back to the East Coast. Rail was built in the mid 19th century joining it to growing web of rail along the east coast. It has a state forest to the north of it that similar to the Huron-Manistee National Forests and resembling something out of that Robert Frost poem "Road not taken." To the city's south bordering the lake is an airport.
That gives you a lot of clues as to where it might be located. But for something more concrete, in our notes Valerie and I have it sitting on the shores of Lake Michigan in Michigan, probably around South Haven through to Ludington.
Erie is a good guess though and similar to Erie's Presque island and pennisula, the city has a seawall linking the city to a small island providing a sheltered harbor the seawall however links the island on the north side not south.
