By law in the state of Illinois, if more than one resident shares a sewer line, whose responsibility is it to maintain? Shouldn't the village maintain it since it runs through two backyards and I cannot legally go on private property to fix it?

In Florida If the sewer line is used jointly and it's on private property then the expense should also be shared jointly. We have Illinois plumbers here that can answer this much better then me.
How about it guys? Tom