Loi is a surname of various origins. It may be a Punjabi surname common among (and exclusive to) Jatt Sikhs in Punjab, one of three Chinese surnames (, , ), or a traditional surname from Sardinia.
Loi may be the spelling of three Chinese surnames, based on their pronunciation in different varieties of Chinese; they are listed below by their spelling in Hanyu Pinyin, which reflects the Mandarin Chinese pronunciation:
The Chinese surname meaning "thunder" is spelled in Vietnamese as Lôi (, that being the Sino-Vietnamese pronunciation of the original Chinese character).
Loi is a surname found in Punjab, it is a common Sikh Jatt surname used by farmers/landowners. The surname Loi only belongs to the Jatt caste within the Sikh and Punjabi community.
As an Italian surname, Loi appears to have originated as a shortened form of some given name, possibly the Sardinian Balloe/Balloi, or the Sicilian Aloi (the local form of the name Eligio).
Loi may also be a Greek surname.
In Italy, 2,716 families bore the surname Loi, with the great majority of them (2,061, 76%) located in Sardinia, and only 10 (0.5%) located in Sicily.
According to statistics cited by Patrick Hanks, there were 282 people on the island of Great Britain and one on the island of Ireland with the surname Loi as of 2011. There was one person with the surname Loi on the island of Great Britain in 1881.
The 2010 United States census found 1,357 people with the surname Loi, making it the 19,814th-most-common name in the country. This represented an increase from 985 (23,922nd-most-common) in the 2000 Census. In both censuses, slightly fewer than nine-tenths of the bearers of the surname identified as Asian, and between six and eight per cent as White. It was the 1,056th-most-common surname among respondents to the 2000 Census who identified as Asian.