According to the 2021 census gazetteer files, Dahlgren has a total area of 1.02 square miles (2.64 km2), all land.

[4] The area around present-day Dahlgren was known in the 1860s as the Shelton Precinct in Hamilton County before townships were formally established.

In 1869 surveyors for the St. Louis & South-Eastern Rail Road (predecessor to the Louisville and Nashville Railroad) referred to the future town site as "Little Prairie."

[5][6] The village was named for John A. Dahlgren (1809–1870), a U.S. naval officer prominent during the American Civil War.

[7] On March 29, 1872, the official founding date of the village, A. M. Sturman executed a Deed of Dedication whereby he ceded 1 square mile of land centered on present day Main and 3rd Streets to formally layout the town.

The Evansville Western Railway (EVWR) (formerly CSX Transportation) provides freight rail service to Dahlgren.

CSX divested 120 miles (200 km) of rail line (from Howell Yard in Evansville, Indiana, to Okawville, Illinois) to the Paducah and Louisville Railway (PAL), an operating entity of Four Rivers Transportation, Inc.

Interstate bus service is available in Mount Vernon, Illinois, 15 miles (24 km) to the northwest.

There is no current newspaper of record as the weekly McLeansboro Times-Leader formerly published in the county seat folded in 2018.

Other daily newspapers available for home delivery in the area include The Morning Sentinel (Centralia & Mt.

Vernon, moved its transmitter northwest of Breese, IL in the St. Louis, MO DMA and is no longer available over-the-air in Dahlgren.

Viewers with a rotator and suitably elevated antenna can also receive virtually all over-the-air broadcasts from Evansville, Indiana.

Hamilton County Communications (a wholly controlled subsidiary of the Hamilton County Telephone Cooperative - HCTC) acquired the cable-operating rights upon Longview's demise and operated an IPTV-based television service under the Futiva brand until 2019 when HCC exited the business.

The village provides basic utility services including water, sewer, and gas and contracts on a fee-for-service basis with a third party for refuse removal.