Every year in Los Angeles, there is a Doctor Who convention called Gallifrey One and we decided last summer to go (actually it was April or May). The convention has a bunch of cast members (from classic and new Who) who sit on panels, get interviewed, and even attend receptions where you get to meet them in a smaller setting.
About 3700 people attend (apparently this is a small number compared to other SciFi type conventions). They come from all over the US and Canada. They dress in regular clothes and in costume. Here are a few of the costumes. For those of you who know Doctor Who I'm sure the costumes are familiar and need no captions. For those of you who don't know, I don't imagine you care, but I'm putting the captions anyway.
Queen Elizabeth I (using her ipad)
Clara in the TARDIS
Amy and her centurion..
Madame de Pompadour