For example, F. C. Ridel's Grammaire Coréenne published in 1881. https://imgur.com/oSxewU0 Also, Independence Newspaper(獨立新聞), the nation's first Korean-only newspaper in 1896. https://imgur.com/7bruwF7
"2015년 인구주택총조사 전수집계결과 보도자료" [Results of the 2015 Census of Population and Housing survey]. Korean Statistical Information Service. Retrieved 28 May 2019.
"로마자성명 표기 변경 허용 요건". Ministry of Foreign Affairs. 2007. Retrieved 2019-05-17.
surname.info
Surname Info. "I." (Korean language site - "이" is spelled phonetically as "I") The specific reference is at the very bottom of the main entry, under the section "[인구 (人口) - 경주, 월성]," which gives both the 1985 census population of the clan at 1,217,279 individuals, and the 2000 population at 1,424,866 individuals. http://www.surname.info/i/gyeong_ju.html