[4] It is best known for being the home of the East Texas Yamboree and the birthplace of popular music singers Don Henley of the Eagles band and Johnny Mathis, as well as blues musician Freddie King.

Founded in 1846, the city's namesake is former Secretary of the Navy Thomas Walker Gilmer.

According to the United States Census Bureau, the city has a total area of 4.6 mi2 (12.0 km2), all land.

Gilmer is part of a larger area known as the East Texas Piney Woods.

The climate in this area is characterized by hot, humid summers and generally mild to cool winters.

[5] As of the 2020 United States census, 4,843 people, 1,778 households, and 987 families were residing in the city.