Four crews put out the blazing hay while farm staff moved cattle from the neighbouring building.
The alarm was raised at the farm at Edgton, near Craven Arms, at about 12.20pm yesterday.
Steve Purslow, Shrewsbury station manager, said: "The first crew on the scene was from Bishop's Castle.
"On arrival they were faced with a hay barn completely involved in fire.
"Due to the rural location they had to send for more crews."
He said to get the amount of water needed they had to lay a makeshift water main down the winding country lanes around Edgton.
"It's proved to be very difficult," he said, "There were pumps from Bishop's Castle, Craven Arms, Clun and Church Stretton, a water carrier from Bridgnorth plus a light pumping unit from Shrewsbury.
"Luckily that has one and a half kilometres of hose.
"That allowed us to control the fire and protect the surrounding buildings.
"There were a lot of cattle in the building next to it – we managed to save those and get them moved.
"We're still investigating the cause, but we don't believe it to be suspicious."
He said the barn was severely damaged, but the surrounding buildings were not.
Fire officers stayed at scene damping down into the evening.