Sidney George Fisher (March 2, 1809 – July 25, 1871) was a Philadelphia lawyer, farmer, plantation owner, diarist, political essayist and occasional poet.

Sidney George Fisher was the eldest of three sons born to James Logan Fisher and Ann Eliza George. His father died when he was five and his mother when he was 12, leaving Sidney and his brothers a considerable inheritance. The three boys—Sidney, James, and Charles—went to live with their aunt Sarah Logan at the family's ancestral home, Wakefield, in Germantown. He was educated at Germantown Academy and Dickinson College.

Fisher read law under Joseph Reed Ingersoll, and prospered as a lawyer, but by the mid-1850s he was practicing law only when it pleased him, and took up more congenial pursuits. Though he begrudged the practice of law, he had friends and relatives in the legal profession, whom he aided infrequently when his assistance was requested.

Fisher wrote several books and delivered numerous talks. Of considerable interest was his highly sought after diary, full of keen, witty and unabashed observations—and often criticisms—about individuals from society, national politics, and his own day-to-day activities. He was largely disconnected from the world of work, except for when he reluctantly agreed to practice law. He did not need to make money (though he never felt his income sufficient), so his views of land speculation and the war against the Second Bank of the United States, the panics, and the commercial activities of those around him are particularly thought-provoking.

Fisher inherited a plantation, Mount Harmon, on the Sassafras River in Cecil County, Maryland, from his maternal grandfather and namesake, Sidney George. He leased the land to farmers who lived there with their families and paid him rent. Although he was a gentleman farmer, Fisher advised his fellow farmers to diversify beyond grain by seeking out produce that would fill huge demand. During his ownership of Mount Harmon, Fisher wrote about the plantation in his diaries. The originals now reside with the Philadelphia Historical Society. They were published as Mount Harmon Diaries of Sidney George Fisher 1837-1850, edited by W. Emerson Wilson.

Fisher was elected to the American Philosophical Society in 1860.

Fisher married Elizabeth Ingersoll, granddaughter of Jared Ingersoll and daughter of his mentor, on May 28, 1851. The couple had one son, historian Sydney George Fisher (1856–1927). A few years after his marriage, the family moved to a country residence owned by the Ingersolls called "Forest Hill", located about four miles north of Philadelphia, and that remained Sidney Fisher's home until he died.

As a fervent anti-Democrat, Fisher was a de facto Whig. He lent his support to candidates who opposed the Jacksonian Democrats in national elections, and remained an ardent anti-Democrat his entire life.