Harvey Kilpatrick Stuart O'Melveny, known as H.K.S. O'Melveny, (1823–1893) was a Circuit Court judge in Illinois and a Superior Court judge in California during the 19th century. He was president of the Los Angeles, California, Common Council—the legislative arm of the city—in 1871-72.
O'Melveny was born on March 5, 1823, in Elkton, Kentucky, the son of William O'Melveny and Susan McKee, Presbyterians who immigrated from Ireland. He had five brothers and five sisters. The O'Melvenys moved to Southern Illinois when Harvey was three years old, and he spent his youth in Waterloo, Illinois, where he attended school. Discipline was strict in the family, and Harvey once recalled that he was once "thrashed" for whistling on Sunday, the sabbath.
A "family tradition" held that H.K.S. O'Melveny attended McKendree College at Lebanon, Illinois. At the age of 20 he began to read law under the tutelage of James Shields and Governor William H. Bissell, and was admitted to the Illinois bar in 1846.
In summer 1850, he married Anna Wilhelmina Rose, sister of the noted California pioneer and state senator, Leonard John Rose. Their children were Edward H., Henry William, Anna R. (Mrs. George Safford) and Adele (Mrs. Calvert Foy). In time, the entire family moved to Los Angeles.
O'Melveny was stricken with his final illness ("apoplexy") while he was walking on Spring Street on November 7, 1893; he was taken to the home of his son Henry, 1148 South Pearl (Figueroa) Street (corner of 12th Street), where he died on November 18. Funeral services were held in the Pearl Street home on November 20.
O'Melveny began his law practice in 1846 in Belleville, Illinois, and in 1849 he crossed the Great Plains on horseback to reach Sacramento, California, on August 4 of that year; he formed a law partnership with Murray Morrison, whom he had known in Kaskaskia, Illinois. In Sacramento he was appointed recorder of land titles for the Sonoma District by General Bennett Riley, the military governor. Ill health prompted O'Melveny to move to Benicia, and practiced before a Major Cooper, "judge of the first instance under the Mexican regime (corresponding nearly to our justice of the peace.)"