It was built in 1861 and was listed on the National Register of Historic Places in 1977 as a part of the County Courthouses in Iowa Thematic Resource.

The Old Allamakee County Courthouse is a two-story, brick, vernacular Greek Revival structure.

It features cornice work and paired brackets on both stages, louvers at the bell chamber, and a finial on top of its tin-covered dome.

Other decorative elements of the building include a classical pediment with a returned cornice and paired brackets, simple brick pilasters on all four sides of the building, and stone window sills and lintels.

Even though the interior was altered in the 1960s, it still retains tin ceilings, most of its original woodwork, and a divided-flight stairway with large wooden newel posts and slender spindles.