It was designed by George M. Coombs of Lewiston and built in 1898, replacing the school's original 1864 building, but includes an ell dating to 1888.

Merrill Hall is set on a rise facing Farmington's Main Street to the west, just south of the town's central business district.

It is a Romanesque Revival building 2-1/2 stories in height, constructed of brick with granite and wood trim.

To the rear of the building is an attached 2-1/2 story brick ell, which predates the construction of the main block.

It was originally housed in the old wood-frame Farmington Academy building, to which the present rear ell was added in 1888.