This is actually a very interesting question, as this play, plot wise, does not seem to have the normal structure of a text in having a character that is trying to achieve something that other characters are opposed to. In fact, Wilder seems to have produced a play that focuses on the normal cycle of human life and the way that death interrupts that cycle so often. This makes me think that the protagonist is not so much one character but all of the humans who are presented in this play, and that the antagonist is death, who cuts their lives short and ends their existence. Again and again the Stage Manager refers to the passing of time, such as in the following comment when he talks about marriage:
I've married over two hundred couples in my day Do I believe in it? I don't know. M ... marries N . . millions of them. The cottage, the g-cart, the Sunday-afternoon drives in the Ford, the first rheumatism, the grandchildren, the second rheumatism, the deathbed, the reading of the will,... Once in a thousand times it's interesting.
There is constant reference made to the cycle of life and what happens as we gradually grow up and get older. Without a traditional plot, it seems that the only antagonist in the play is the force of death that terminates our lives.
I suggest that it is the Stage Manager who is the protagonist of "Our Town." It is his motivation to describe the region and to introduce and explain the townspeople that drives the entire play. He does not have a serious antagonist, but he has the difficulties that come with being a stage manager and a narrator. For example, one of the characters he has recruited is a college professor who is too long-winded and has to be cut short, while another is the newspaper editor who doesn't show up on time. The Stage Manager also has difficulties in explaining what places are represented on a barren stage, and he has some difficulties with his own memory. This is a post-modernist type of play, although the story itself is extremely conservative and conventional. The audience gets the impression that the Stage Manager is trying to put a play together and that he does not even have complete control of the characters.