Among the buildings in the district are ones dating back to 1788,[1] the year in which Marietta was founded as the first white settlement in what is now Ohio.

[2] Among its most significant buildings are the Rufus Putnam House and the Ohio Company Land Office, which are also separately listed on the Register.

[3] When the district was added to the Register in 1974, it encompassed an area roughly bounded by the Muskingum and Ohio Rivers and Warren, Third, Fifth, and Sixth Streets.

In 2001, some of its original boundaries were slightly reduced, but it was also expanded greatly to include an area roughly bounded by Marion, Montgomery, Ohio, Greene, Butler, and Second through Ninth Streets, and the Ohio and Muskingum Rivers.

The resulting district encompasses over 900 acres (360 ha) and includes over two thousand contributing properties.