Haplogroup I is found at very low frequencies (generally < 3%) throughout Europe
, Middle East
and South Asia
. It is nearly absent in parts of Europe (Iberia, South-West France, Ireland) and strongest in Iceland (> 5%), Scotland, Norway, southern Finland, Ukraine, Greece and western Anatolia.
A February 2009 study found that Lemkos (a sub- or co-ethnic group of Rusyns) in the Carpathian mountains have the "highest frequency of haplogroup I (11.3%) in Europe, identical to that of the population of Krk Island (Croatia) in the Adriatic Sea".
Haplogroup I has also been observed at a frequency of 8.3% in Russians from Oryol Oblast.
The frequency of haplogroup I may have undergone a reduction in Europe following the Medieval age. An overall frequency of 13% was found in ancient Danish samples from the Iron Age to the Medieval Age (including Vikings
) from Denmark
compared to only 2.5% in modern samples. As Hg I is not observed in any ancient Italian, Spanish, British, central European populations, early central European farmers and Neolithic samples, according to the authors "Haplogroup I could therefore have been an ancient Southern Scandinavian type “diluted” by later immigration events".
According to Melchior et al. (2008), "The observation of haplogroup I in the present study (<2% in modern Scandinavians) supports our previous findings of a pronounced frequency of this haplogroup in Viking and Iron Age Danes.". 
Outside of Europe, the highest frequencies of mitochondrial haplogroup I observed so far appear in the Cushitic-speaking El Molo (22%) and Rendille (15%) in northern Kenya, Sindhis from Pakistan (8.7%), Kurds from western Iran and Turks from eastern and western Azerbaijan (both 5%), and Mazandarians from northern Iran (4.5%). Found in Svan population from Georgia(Caucasus) I* 4,2%