USPS - the post office (it was either that or the undertaker!)
The main post office, just east of the square opened in 1963. Doesn't that architecture scream 60s? It is an unusually busy place most of the time as we've almost outgrown it.
Until 1963 it was in a building that we've seen before, a building that became the library after the post office move in 1963 and later, in 1990, the Marietta Museum of Art.
Here are four upstanding young ladies standing on the steps of that new post office in 1910 just after it opened.