Surprisingly, the origin of numpty is Georgian!

The current surge in popularity is reflected in the fairly recent 1985 publication of Michael Munro’s collection of Glaswegian dialect. This is not when the word first appeared, however, rather when it saw a resurgence in popularity. Its origin is from the early 18th century.

As early as the 16th century, the term “numps” was used to describe a silly person or someone acting dimwittedly. It’s possible the “numpty” variation was in usage even then, but the first recorded usage was in 1733. We see it and variations of it in other publications in 1785, 1794, 1795, and 1797.

Either the popularity waned after that, to resurface in the 1980s, or it was used in speech but not in writing until we see it appear again in the 20th century. The meaning hasn’t changed since the Georgian era, and it is now an exceeding popular slang term one is apt to hear often, especially in the northern regions of England and most certainly in Scotland where it’s most popular. 

Enjoy this exploration of the origins:

King's College, The Origins of the Word Numpty