According to the 2021 census gazetteer files, Palmer has a total area of 1.00 square mile (2.59 km2), all land.

Sometimes a railroad or highway built through a small town causes that place to grow; It was not so with Palmer.

[citation needed] The coming of the railroad in 1870 sounded the doom of Harpers Ferry, located on the Old Edwardsville Road.

Harpers Ferry hosted a post office for Star Route pony express, a mill for grinding grain, a wayside station for the Stagecoach, and a few stores.

Boyd and Simpson erected the first store in 1869 and the firm of Starke and Hailey put in a stock of goods.

James McCauley opened the second store and when the first post office was established in 1870 it was housed in his building with G.E.

At one time it was the dream of a group of citizens in the area to sink a coal mine, bringing industry, employment, and fuel to the community.

The site selected to sink the mine was in the southwest edge of town, on the north side of the railroad.

The cost of sinking the shaft was $2.50 per foot, and it is believed that the depth was approximately 500 feet (150 m).

About 1932, Illinois State Route 48 was constructed through Palmer - part of it over the top of the old mine.

Approximately 190 truckloads of slag, rock, and dirt were hauled to the site and the shaft was filled at an estimated cost of $30,000.