Huishui Miao language
Huishui Miao, a.k.a. Huishui Hmong, is a Miao language of China. It is named after Huishui County, Guizhou, though not all varieties are spoken there. The endonym is Mhong, though it shares this with Gejia and it is simply a variant spelling of Hmong. 

Huishui was given as a subgroup of Western Hmongic in Strecker (1987). Matisoff (2001) split it into four separate languages, and, conservatively, did not retain it as a group.

Demographics
Below is a list of Miao dialects and their respective speaker populations and distributions from Li (2018), along with representative datapoints from Wang (1985).

According to Sun (2017), the northern dialect of Huishui Miao is spoken in the following townships by a total of approximately 50,000 speakers.

Guiyang City: Gaopo 高坡
Huishui County: Yangchang 羊场
Guiding County: Tangbao 塘堡, Pingfa 平伐, etc.

References

West Hmongic languages
Languages of Guizhou