Family name Sinlong (Sinlong 
) , throughout the world, is a very rare last name. The surname Sinlong is characteristic of Portugal, where it is a rare surname, Thailand, where it is a very rare surname, and Philippines, where it is an extremely rare surname. Measured by absolute frequency, this name is the most popular in Portugal, Thailand, and the United States. Very seldom, Sinlong is the forename as well as the last name.