I suspect that the settlers from the early 1800s would have been overwhelmed by the notion that people would advertise by mail. Getting the mail was a fairly amazing feat.
According to one essay I read, the mail service was seen by President Washington as something much more than sending letters and XFinity ads; George believed that the information dispensed by the post office was necessary for the stability of the union. In his address to Congress in 1791:
The importance of the post-office and post-roads … is increased by their instrumentality in diffusing a knowledge of the laws and proceedings of the Government, which while it contributes to the security of the people, serves also to guard them against the effects of misrepresentation and misconception.
The first postal service in the Indiana territory is vaguely around the year 1803, mostly from Vincennes to Louisville and vice-versa. Not much population elsewhere. By 1814 or so, the post-roads concept (roads designated and funded by Congress to deliver the mail) had caught on and places like Fairfield were on the path to be served.
By 1820, Fairfield had its own post office, according to an old Atlas Gazetteer. Charles Shriner was the first postmaster. I can't find how long this post office functioned but I think it may have at least been until the 1880s. Exactly where it was located is unclear but I would imagine it was in one of the general stores in the downtown area. I have heard that it was in a little house just to the north of the Odd Fellows lodge.
From the Indiana History Magazine:
From 1834-38, Route No. 3,025 ran from Richmond to Cincinnati, the mail being transported twice a week, in stages from Richmond to Brookville, and three times a week, in stages, from Brookville to Cincinnati. Abner McCarty received $1.200 for the performance of this duty. The towns along this route that received mail from these stages were. Abington, Brownsville, Liberty, Dunlapsville, Fairfield, Brookville, Cedar Grove, New Trenton, Harrison (Ohio), Clark's Store, Miami and Cheviot. The total distance was 76 miles.
Those early days were odd. The recipient paid for the delivery, and it wasn't cheap. This was long before the introduction of the stamp.
First 40 miles - 8 cents
40 to 90 miles - 10 cents
90-150 miles 12.5 cents plus
25 cents for distances of 500 miles.
In 1801, that was a lot of money. Bad weather, accidents, Indian attack, illness, drunkenness, and willful neglect easily upset the schedules. There were frequent complaints by the populace and the postmasters. The carriers weren't inclined to be too concerned about complaints.
Sources for this item are diverse.
-- Benjamin Franklin is credited for developing the American postal service. Thank him for your Christmas cards.