So is it theatre or theater? Ok, so it isn't the most important question, but none the less it is one that people are really split on. But which one is correct? Theatres (or theaters) around Chicago are also split on this as well. For example, you can go to the Goodman Theatre or the Victory Gardens Theater but which one is correct?
According to a 1960's article in "Theatre Survey" by Francis Hodge, "theater" is a result of Noah Webster's push in the late 1820s to create an American language purified of English spellings. Webster was one of the early publishers of dictionaries of the English language and in 1828 he published the first edition of his American Dictionary of the English language. Webster changed the spelling of many words in his dictionaries in an attempt to make them more phonemic and less British. This is also when many other words changed that Webster deemed to be too British for the new American democracy, such as "colour" becoming "color", "centre" becoming "center", "honour" becoming "honor" and "grey" becoming "gray".
Since the American theatre (or theater) at this time was still dominated by British actors and managers, along with American actors and managers trying to suggest that theater (or theatre) was a high class art, the practitioners rather stubbornly clung to the British spelling. There have been a lot of attempts to differentiate usage ever since, but really whatever you choose to use will work.
Today, it is primarily considered that the word theatre/theater is in most cases interchangeable. Most American theater companies use the “re” ending and often you’ll see the “re” when the word refers to the art form or actual companies, but “er” when it refers to the building itself. So with this "rule" in mind we would say the Goodman Theatre is a great theater.
So there is no clear cut right or wrong way to spell theatre/theater, so each can use their own artistic liberty and use whichever they prefer. I should note, this holds true for this site as well, so feel free to go to either theatreinchicago.com or, if you prefer, theaterinchicago.com.