I don't know, I think the longer I live in the UK, the more confused I get by that question because I need a point of reference...where am I from, now, or when do you mean? lol
For instance, a couple of years back when I lived in Erdington (a part of Birmingham) an American friend (who also lived in Erdington) and I hopped a bus to another part of the city to go to a free museum. When we got there, we found out there was also a free tour, so we decided to be back at the start of the tour at the appointed time (had a cup of tea first!). When we got back for the tour, we learned we were the only ones on the tour, which was ok.
The tour guide started out by telling us a bit about the history of the property, and we had a nice little chat, asked a few questions, etc. Then, he asked us where we were from. There was a pause while we both went through the point of reference thing in our heads, and then we answered him in unison - 'Erdington!' All three of us started laughing, with him saying he hadn't been in Erdington for a few years and hadn't realised the accents had changed so much.
Still, if people have cottoned on that I'm American, then I say I'm from Wisconsin...I use a city, Chicago, as a point of reference as to where the state is! Except I'm running into more and more people in this country who have a fairly good idea that Wisconsin is one of those northern states sort of in the middle of the country, by those big lakes. Maybe it's because the only 'big' city I ever lived in was Minneapolis, but I just don't get into trying to describe where in Wisconsin I'm from unless I run into someone who actually starts naming Wisconsin cities, and that's rare...even for Wisconsinites!