Consider this for what it is worth: I grew up in southwestern Michigan in
the 1950-60's. The room we watched TV in was called the den, while the
living room was where the adults sat for formal occasions. We never used
the living room otherwise. As far as I know most people had "dens" in
their homes. However, when people started building ranch-style homes,
the "dens" became family rooms and seemed to mostly be just off from
the kitchen or down a flight in a split level.
the 1950-60's. The room we watched TV in was called the den, while the
living room was where the adults sat for formal occasions. We never used
the living room otherwise. As far as I know most people had "dens" in
their homes. However, when people started building ranch-style homes,
the "dens" became family rooms and seemed to mostly be just off from
the kitchen or down a flight in a split level.