Battalion Chief Edward Voss said the Clock House, one of a collection of vacant homes in the Heidelberg Project, was found in flames Sunday night, the Detroit News reported Monday.
The display could not be saved even though fire fighters arrived within 5 to 7 minutes, Voss said.
Remaining projects are the Numbers House, the Dot House and the Teddy Bear House. Two small fires damaged the Numbers House earlier this year.
Project founder Tyree Guyton was near tears as he watched the fire turn the Clock House into ashes. He said he might leave the charred remnants of the house as "a part of my protest" that was his inspiration for the project.
Guyton created the project in 1986 by decorating abandoned homes.
The last fire, at the War Room, happened Nov. 28, the Detroit Free Press reported.
Project organizers and supporters have been raising funds to increase security patrols and add lighting and security cameras to the project on Detroit's poor east side. So far, more than $33,000 has been raised online toward a goal of $50,000.
Detroit arson investigators have been working with the U.S. justice Department and the Bureau of Alcohol, Tobacco, Firearms and Explosives to determine who set the fires. Detroit fire officials said in November they had identified a person of interest.
The ATF announced a $5,000 reward earlier this month for information leading to the arrest and conviction of people involved in the fires, the Free Press reported.