According to Official Guinness Records,
The longest tongue on a dog measures 18.58 cm (7.31 in) and belongs to Mochi, a female St. Bernard owned by Carla and Craig Rickert (both USA) and was measured in Sioux Falls, South Dakota, USA, on 25 August 2016.Mochi was rescued by the Rickert family when she was two years old. "We love her unconditionally despite that crazy, long tongue that causes people to stare and laugh," said her owner Carla Rickert.
For a complete list of 2016 records, please visit 2016 Guinness Records in United States.