This question is specifically about the pressure at ground level.
More specifically, I am looking for the average pressure in places where humans commonly live. Since the average elevation of homes is higher than sea level, the average pressure is bound to be lower.
Even better would be a range of pressures to reasonably expect in places where people live. Bonus points for a probability distribution, but that is outside of the scope of the question.
At relatively low altitudes, where most people live, the variation of pressure with the height is approximately linear. Therefore, the average pressure can be approximated by applying the barometric formula to the average ground elevation at places where people commonly live. So the answer to this question depends on the answer to "What is the average elevation where people commonly live?"
A refinement of the barometric formula is the standard atmosphere. Online implementations of standard atmospheres can be found here (ICAO Standard Atmosphere) and here (US 1976 Standard Atmosphere), the latter one being particularly immediate and detailed.
For an elevation of 100 m, these give a pressure of 1001 hPa, roughly one percent below 1 atm.