Longmen County, alternately romanized as Lungmoon, is a county of Guangdong, China, administered as part of the prefecture-level city of Huizhou. In 2020, Longmen County had a population of 319,183 residing in an area of .
The northernmost county-level division of Huizhou, Longmen County borders Dongyuan County to the east, Boluo County to the south, Zengcheng and Conghua to the west, and Xinfeng County to the north.
Longmen County comprises two subdistrict, seven towns, and a township:
In addition to Mandarin, there are several local languages spoken within Longmen County: Cantonese, Hakka, Minnan, and ethnic-minority languages such as Yao and She.
(Wuhan-Shenzhen), (Guangzhou-Heyuan) and (Shantou-Zhanjiang) pass through the county. The Shaoguan-Huizhou Expressway is currently under construction.