The Washington Street office of the onetime Ypsilanti Gas Company, whose plant was on the northeast corner of Huron and Forest. This is the downtown business office, where, if you were a miser like DD too cheap to spring for a stamp, you could go to pay your bill.
The photo is dated 1912. This may be incorrect as the city seized municipal control of the gas plant in 1914, holding it until after WWII. The inscription continues: "House in background: 212 Pearl. Later moved to 921 Sheridan (Ward Roper House). Genevieve C. Cross & Phil Duffy, in front of gas company, 27 N. Washington."
Note that in the reflection of the window you can see the sign for Ypsilanti's storied "ARK" secondhand store/junk shop/nexus of questionable activities.
I guess you could say the northwest corner of Washington and Pearl is still a place with a lot of energy...