Cognomen Thennakoon (Thennakoon 
) , worldwide, is a common last name. The surname Thennakoon is habitual in Sri Lanka, where it is quite a common surname, Qatar, where it is quite a rare surname, and Kuwait. In absolute terms, it most frequently occurs in Sri Lanka, United Arab Emirates, and Saudi Arabia.
| VARIANT | COUNTRY |
|---|---|
| Thennakoon | Saudi Arabia, Indonesia, Sri Lanka, United Arab Emirates, Kuwait |
| daya thennakoon Sri Lankan actor, LK (b. 1941) |
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| keerthi thennakoon Sri Lankan governor |
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| kavindya thennakoon LK (b. 1995) |
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Dan, Tilan, Namal, Nimal, Nuwan, Inoka, Ishan, Isuru, Oshan, Udaya, Thara, Udara, Menaka, Minidu, Sanath, Salika, Saliya, Samith, Sajith, Suresh, Suneth, Mahesh, Jerom, Gihan, Gayan, Madu, Arju, Amal, Manoj, Saman, Anura, Anupa, Aruna, Amila, Amith, Asiri, Asela, Akila, Ajith, Kalpa, Kamal, Kasun, Ranga, Rohan, Dilan, Dulaj, Sumith, and Sugath