Harrison Gray Otis Blake (March 17, 1818 – April 16, 1876) was a U.S. Representative from Ohio.
Born in Newfane, Vermont, Blake moved to Salem, New York, and in 1830 to Guilford, Ohio. He attended the public schools. He studied medicine at Seville for one year. He moved to Medina in 1836 and engaged in mercantile pursuits. He also studied law. He was admitted to the bar and commenced practice in Medina. He served as member of the State house of representatives in 1846 and 1847. He served as member of the State senate in 1848 and 1849, serving as its president.
Blake was elected as a Republican to the Thirty-sixth Congress to fill the vacancy caused by the death of Cyrus Spink. He was reelected to the Thirty-seventh Congress and served from October 11, 1859, to March 3, 1863. He was not a candidate for renomination in 1862 to the Thirty-eighth Congress. He entered the Union Army in 1864 as colonel of the 166th Ohio Infantry. He declined the appointment of Governor of Idaho Territory. He resumed the practice of law. He was also interested in banking and mercantile pursuits. He served as delegate to the Loyalist Convention at Philadelphia in 1866. He died in Medina, Ohio, April 16, 1876. He was interred in Spring Grove Cemetery.