The earliest references to coffee as "cold" in both Near Eastern and European traditions--all the way back to the 16th and 17th centuries respectively!--can't be taken in our modern sense. Despite being served as a hot liquid, coffee was initially considered "cold and dry" according to humoural theory.

That is, hot/cold/wet/dry described properties of food and drinks that determined how they affected the human body when consumed, by affecting the four humours. The human body, and human actions: the coldness and dryness of a consumable like coffee was thought (again, not what you'd think from "cold") to increase blood flow, thus increasing sex drive!

In the Near East, official moral problems with the supposed aphrodisiac property of coffee led to results like:

• the ulama of Mecca banning coffee in 1511, only to find everyone who had been involved in the ban being removed from their positions by 1512
• unveiled women selling coffee in the streets barred from doing so in 1525, but almost immediately encouraged to start selling it again as long as they veiled their heads
• the Ottoman government banning the sale of coffee in Mecca in 1544 only for the Meccans to say, "Right, about that."

In Europe, official moral problems with the supposed aphrodisiac property of coffee led to results like:

• rebranding coffee as "hot and wet"

(Meanwhile, chocolate drinks--which were originally consumed cold, in point of fact--humourously reversed the trend from hot and wet to cold and dry, and the association between chocolate and sex endures today.)

For actual temperature-cold coffee, however, we have to jump ahead a couple of centuries to 18th century Italy. The sale of sorbetti--ice/snow drinks and foods--exploded at the end of the 16th century into the 17th. This marked the invention of a process involving salt or saltpetre to produce artifical snow, thus making icy drinks or foods without needing to import ice.

Initially, this meant fruit...sorbet...in particular. By 1775, however, Neopolitan doctor Filippo Baldini described three types of icy concoction popular in the city: fruit sorbets, milk-based drinks, and "aromatic" icy drinks made of snow and cinnamon, chocolate...or coffee.

But even then, bemused travel writers were remarking on how iced concoctions were the drink vice of the Italian lower classes while the British went for many and diverse types of hard liquor.

Thus, the American fascination with iced coffee goes back to the soda fountains of the late 19th century (perhaps related to the influx of Italian immigrants; perhaps not--the idea of just pouring coffee over ice is a little earlier, but it's hard to say how widespread it was given the lack of easy access to ice for most Americans). These restaurants plied their soda wares by adding various flavored syrups to soda water--obviously Coca-Cola being the most enduring and famous. By the turn of the 20th century, however, distilled coffee syrup was among them. Coffee syrup might be added to soda water straight up, to egg creams, or simply to milk.

So by 1959, there were a whole rainbow of ways Americans could consume their coffee cold--in the temperature sense, that is. For that other kind of cold, they'd still want to look elsewhere.

Hopefully, I can give a sufficient enough answer for you!

First, perhaps it's important to look at iced coffee's older brother, the ubiquitous iced tea. Iced tea had been around in the U.S since at least 1860s as it appears in a few cookbooks from the era, being a novelty at first but the 1870s it had been pretty widespread. Finally, by the 1904 World's Fair, Iced Tea had become pretty popular.

Now onto the coffee. Pre-WWI, coffee had been around the U.S but it was not as popular as a drink as it is today. When the U.S entered the war, American troops soon began developing a taste for coffee as it was commonly served in European canteens found throughout the front. By the time WWI ends, American troops returned home having a taste and desire for the drink.

By the 1920s rolls around prohibition is in effect and suddenly we see the rise of cafe culture in the U.S to replace taverns. It was a legal way of going out and socializing while also providing a similar experience (drinking something, talking, ect). It is also in the 1920s that we see the first widespread ad campaigns for "iced coffee".

By the 1950s coffee is ubiquitous in every corner cafe, restaurant and home in America. Even instant coffee is being marketed as something that "every man can make" regardless of skill in the kitchen. It's even being endorsed by celebrities at this point. The term "coffee break" is even coined at this point in time as coffee and the working class go hand in hand.

This is where we get to iced coffee. People would have already been at least somewhat familiar with iced coffee since for a while but mostly it would have been a novelty drink. But because of coffee's prevalence as a proletariat drink in the 1950s vendors of coffee start selling it in different ways. In hotter climates, iced coffee would provide the same caffeine benefits of a 'regular' coffee but in a refreshing new way.

So to answer your question: In 1959 most Americans would probably know what an Iced Coffee is, though it might still be somewhat of a novelty.

Sources

• Tyree, Marion Cabell (1878). "Iced Tea". Housekeeping in Old Virginia. Louisville, Kentucky: John P. Morton & Co.
• Ice-cream and Cakes: A New Collection of Standard Fresh and Original Receipts for Household and Commercial Use, Charles Scribner's Sons
• "Iced Coffee Boom Started with Reprint of Recipe Booklet", The Spice Mill,
• Pendergrast, Mark. Uncommon Grounds: The History of Coffee and How It Transformed Our World. New York, NY: Basic Books, 1999.
• Benedict Crowell, Quartermaster Activities in World War I," America Munitions 1917-1918, Government Printing Office, Washington, DC, 1919, archived by the US Army Quartermaster Museum,
• Clarence-Smith, W. G., and Steven Topik. The Global Coffee Economy in Africa, Asia and Latin America, 1500-1989. Cambridge, UK: Cambridge University Press, 2003.