Kynnumboon is a locality in the Tweed Shire of New South Wales, Australia. It had a population of 109 as of the .
The name for this place is likely derived from the Bundjalung language a and is either taken from the word kinnonboon (a type of root) or kingimbon (rock). Alternatively it may have been taken from the Yugambeh dialect word guyahnambuhn which means 'the place of possums'.
As of the 2021 Australian census, 109 people resided in Kynnumboon, down from 134 in the . The median age of persons in Kynnumboon was 54 years. There were more males than females, with 51.8% of the population male and 48.2% female. The average household size was 2.5 people per household.