I'd say 'at the circus'.
I'd use 'in' with 'circus tent', for example.
Saying "performed by the circus" is not really logical to me because a circus doesn't perform. It's the people (and animals) who work at the circus who perform.
But how can I be more clear that in which I can use the word directly, for example, the committee decided to cancel the test, in this sentence committee is just a collective noun, but we can use it with the verbs directly, the circus in Chinese is also a collective noun, it means the people and animals who work at the circus, How can i distinguish it?