Present day Monument, sometimes called Monument Siding, is in actuality Ennis City. The town was platted by John B. Ennis, an attorney from Ottumwa, Iowa who was residing in Oakley at the time of his death and is buried in the Oakley Cemetery. Monument, on the railroad, is an extinct town in the draw west of the US24/K25 intersection west of present Monument.

Post Monument, sometimes called Fort Monument, was on the Smoky Hill Trail, as was Monument Station, an "eating" station of Butterfield's Overland Despatch. When the Kansas Pacific Railroad. (U.P.R.R., Eastern Division) was laid, the name "Monument" was attached to the railroad station which is now extinct. The grade at Monument Station (on the railroad) was too steep for a siding, so the siding was placed approximately two and a half miles east and called Monument Siding and platted as Ennis City.

In 2000, the population of Monument was 144.
An old black and white aerial photo of Monument