The blaze began around 4:30 a.m. inside a small barn once used to milk cows and the structure has since collapsed. No one was hurt.
"I just think it's sad to see something so old like that and beautiful be burned down," said Teresa Fay.
A loft and unique design drew people to the building. In fact, it was so loved--- locals would often take pictures.
"It symbolizes this area is still a rural and part of the country and there's a lot of farms out here," said Mary McColl.
King County sheriff's deputies detained one person found near the blaze as fir fighters pulled up and had called the fire suspicious.
That person was taken into custody, but quickly released because there was no evidence to connect them to the fire.
The fire's origin was traced inside to the southeast corner of the barn, but investigators say they can't find evidence of how the fire started, so the official cause is undetermined.
Locals who loved the structure may never know why it's gone.
"It's really sad," McColl said. "It was a beautiful structure that I believe was really old and part of the history of this area."
Woodinville firefighters say the barn may never be rebuilt because it's in a wetland area.
Park specialists say the Mary Cash Farm will close Tuesday night after dark and may be closed for several days.