This is a bill from the onetime Ypsilanti Gas Company, a municipal utility supplying coal gas to homes all over town for cooking and lighting. The gas generator plant stood at the northeast corner of Forest and Huron, where the DPW yard is now. The plant operated as a municipal utility from 1914, when the city seized control, to the late 40s, when it switched over to natural gas and external ownership.
Here is a DIY bill in case the meter reader couldn't come in your house--presumably meters were indoors in those days--and a lot of moms were at home to be able to let them in. If not, you could just fill in the numbers yourself and mail it in to be billed, as seen on this undated sample which I would guess is from the late 20s-ish (?). ETA: Reader Paul found a date: 1931.