Settlement of the city of Rochester in western New York State began in the late 18th century, and the city grew rapidly following the opening of the Erie Canal. It became a major manufacturing center and attracted many immigrants from Italy, Germany, Ireland, and other countries, as well as a large population of Yankees of New England origin. Rochester served as a center of several reform movements, including abolitionism and women's rights. The city was long associated with the American photography industry and served as the headquarters of Eastman Kodak. Although many Great Lakes industrial cities experienced decline in the post-industrial era often described as the "Rust Belt," Rochester's economy was sustained for several decades after World War II by the presence of Ritter-Pfaudler, Bausch and Lomb, Eastman Kodak, Xerox, Gannett, and other major companies.

Of the 19 places in the United States named "Rochester", at least 8 were named directly after the city, having been founded or settled by former residents. These include: Rochester, Indiana; Rochester, Texas; Rochester, Iowa; Rochester, Kentucky; Rochester, Michigan; Rochester, Minnesota; Rochester, Nevada; and Rochester, Ohio.

Early settlement Following the American Revolution, western New York was opened for development after New York and Massachusetts settled their competing claims for the area in December 1786 through the Treaty of Hartford. Under the compromise, New York retained political sovereignty over the land, while Massachusetts held pre-emptive rights to obtain title from the Native Americans and to own and profit from selling the land.

Phelps and Gorham purchase

On April 1, 1788, Massachusetts' pre-emptive right over all western New York lands—comprising some 6,000,000 acres (24,000 km2)—was sold to Oliver Phelps and Nathaniel Gorham, both of Massachusetts. The sales price was $1,000,000, payable in three equal annual installments of certain Massachusetts securities then trading at about 20 cents on the dollar. The right applied to all land west of a line running from the mouth of Sodus Bay on Lake Ontario, due south through Seneca Lake, to the 82nd milestone on the Pennsylvania border near Big Flats (the "Pre-emption Line"), extending to the Niagara River and Lake Erie (the "Phelps and Gorham Purchase"). To obtain title to the land, Phelps and Gorham were required to extinguish all Native American titles.

When the land did not sell as expected, Phelps and Gorham were unable to fund the extinguishment of Native American titles and defaulted on their second payment in 1790. They lost the right to purchase the pre-emptive rights to remaining lands of the Phelps and Gorham Purchase west of the Genesee River. This land, about 3,750,000 acres (15,000 km2), reverted to Massachusetts, which re-sold the pre-emptive rights to Robert Morris in 1791 for $333,333.33 (about $ today). In 1792 and 1793, Morris sold most of the lands west of the Genesee to the Holland Land Company, though he did not extinguish Native American title to the land until the Treaty of Big Tree in September 1797. Morris reserved for himself a 500,000-acre (2,000 km2) strip approximately wide, extending from Lake Ontario to the Pennsylvania border along the eastern edge of the Holland Purchase, known as the Morris Reserve. At the north end of the Reserve, Morris sold an 87,000-acre (350 km2) triangular tract ("The Triangle Tract") to Herman Leroy, William Bayard, and John McEvers, and a 100,000-acre tract due west of the Triangle Tract to the state of Connecticut. Additional Phelps and Gorham lands east of the Genesee River which had not previously been sold were acquired by Robert Morris in 1791 and re-sold to The Pulteney Association, a syndicate of British investors.

Mill Yard Tract

Before defaulting on the rest of the land purchase agreement, Phelps and Gorham granted a 100-acre (0.4 km2) lot within the Mill Yard Tract at the Upper Falls of the Genesee to Ebenezer "Indian" Allan, on condition that he build a grist mill and sawmill there by summer 1789 (the "100 Acre Tract"). Allan built the mills at the west end of the Upper Falls of the Genesee with the assistance of 14 men. The area at that time consisted of dense forest and swamp, and was affected by rattlesnakes and mosquitoes that spread malaria, then known as "Swamp Fever."

In March 1792, Allan sold the Tract to Benjamin Barton Sr. of New Jersey for $1,250. Barton resold the property to Samuel Ogden, an agent for Robert Morris, who in turn sold it in 1794 to Charles Williamson, agent for The Pulteney Association. On November 8, 1803, The Pulteney Association sold the Tract for $1,750, on a five-year land contract, to Col. Nathaniel Rochester (1752–1831), Maj. Charles Carroll, and Col. William Fitzhugh, all of Hagerstown, Maryland.

Rochesterville and The Flour City

Rochester's early politics were shaped by ethnocultural divisions. Two rival groups competed for influence: Presbyterian Yankees from New England and Episcopalian New Yorkers from New York and Pennsylvania. When Irish Catholics began arriving in large numbers in the 1840s and supported the Democrats, the two Protestant factions formed a common front.Blake McKelvey, "The Irish in Rochester" (1957) Col. Rochester and his two partners left the mill-site undeveloped until 1811, when they completed payment and received the deed. The area's population at that time was 15. They then had the tract surveyed and laid out with streets and lots. The first lot was sold to Henry Skinner, at what is now the northwest corner of State and Main. In 1817, other landowners, principally the Brown Brothers (of Brown's Race and Brown's Square), joined their lands north to the Tract to form the Village of Rochesterville, with a population of 700.

In 1821, Monroe County was formed from parts of Ontario and Genesee counties, and Rochesterville was named the county seat. A two-story brick courthouse in the Greek Revival style was built at a cost of $7,600. In 1823, property belonging to Elisha Johnson on the east side of the Genesee across from the Tract was annexed, expanding Rochesterville to 1,012 acres (4.1 km2) with a population of about 2,500. That year, "-ville" was dropped from the city's name. Also in 1823, the first 800-foot (244 m) Erie Canal Aqueduct was completed over the Genesee, just south of the Main Street Bridge; it was built over 16 months by 30 convicts from Auburn State Prison. In 1822, the Rochester Female Charitable Society was founded. Members paid twenty-five cents per year and contributed provisions, clothing, and bedding collected from the community. Visitors distributed goods and money to the poor of each district. By 1872, seventy-three districts had been established, each with a woman visitor. The organization was instrumental in founding the Rochester Orphan Asylum (now Hillside Children's Center), the Rochester City Hospital (now Rochester General Hospital), the first school, the workhouse, the Home for the Friendless (now The Friendly Home), the Industrial School, and The Visiting Nurse Service.

After the Erie Canal opened east to the Hudson River in 1825, the city's economy and population grew rapidly. By 1830, the population reached 9,200, and Rochester was referred to as "The Young Lion of the West." The city became known as the Flour City, owing to the numerous flour mills located along waterfalls on the Genesee in the area now known as Brown's Race in downtown Rochester. In the first ten days after the canal opened east to the Hudson, 40,000 barrels (3,600 tons) of Rochester flour were shipped to Albany and New York City. Local millers processed 25,000 bushels of wheat daily. In 1829, the Rochester Athenaeum was founded as a reading society, charging members a five-dollar annual fee to attend lectures by speakers including Oliver Wendell Holmes Sr., Horace Greeley, and Ralph Waldo Emerson. The Athenaeum was one of the forerunners of the Rochester Institute of Technology.

In 1830 and 1831, Rochester experienced one of the largest Protestant revivals of the Second Great Awakening, led by Charles Grandison Finney. A contemporary pastor who was converted during the Rochester meetings described the impact of the revival:Hyatt, Eddie (2002), 2000 Years Of Charismatic Christianity, Lake Mary, FL: Charisma House, p. 126, The whole community was stirred. Religion was the topic of conversation in the house, in the shop, in the office, and on the street. The only theater in the city was converted into a livery stable; the only circus into a soap and candle factory. Grog shops were closed; the Sabbath was honored; the sanctuaries were thronged with happy worshippers; a new impulse was given to every philanthropic enterprise; the fountains of benevolence were opened, and men lived to good.

By 1834, some 20 flour mills were producing 500,000 barrels (44,000 t) annually, the population reached 13,500, and the city area expanded to 4,000 acres (16 km2). Rochester was re-chartered as a city, and Jonathan Child, son-in-law of Col. Rochester, was elected its first mayor.

In 1837, the Rochester Orphan Asylum was founded by the Rochester Female Charitable Society. The Asylum was located on South Sophia Street (now South Plymouth Avenue) and later moved to Hubbell Park. Following a fire on January 8, 1901, that killed 31 residents,Blake McKelvey, Rochester History Vol. 17, pg. 15, Jan. 1955. the Asylum was relocated to Pinnacle Hill and reconstructed as a series of cottages called the Hillside Home (now Hillside Children's Center, part of Hillside Family of Agencies). The Charitable Society also founded Rochester City Hospital on Buffalo Street (now West Main Street), on the site of the old Buffalo Street Cemetery. Construction on the hospital began in 1845, but it was not occupied until 1863. By 1838, Rochester was the largest flour-producing city in the world.

The Flower City

In 1830, William A. Reynolds started a seed business at the corner of Sophia and Buffalo Streets (now South Plymouth Avenue and West Main Street). This was the origin of the Ellwanger & Barry Nursery Co., which was eventually relocated to Mt. Hope Avenue, across from Mount Hope Cemetery. James Vick and Joseph Harris also established nursery businesses. Vick used mass marketing and regular customer correspondence to build one of the most prominent seed companies in the United States. His flower garden on East Avenue attracted visitors; the location is now bounded by Vick Park A and Vick Park B. The population in 1830 was 9,207, ranking Rochester as the 25th largest city in the United States. By 1840, the population had grown to 20,191, making it the 19th largest. In 1842, the original aqueduct over the Genesee River was replaced with a larger one slightly south of the first; this latter aqueduct now supports Broad Street.

By 1850, the population reached 36,000, making Rochester the 21st largest city in the United States. Westward expansion had shifted the center of farming to the Great Plains, and Rochester's importance as a flour-milling center declined. Several seed companies in Rochester had grown to become among the largest in the world, with Ellwanger & Barry Nursery Co. being the largest. Rochester's nickname changed from the Flour City to the Flower City. In 1850, the University of Rochester was founded in the U.S. Hotel on Buffalo St, affiliated with the Baptist Church, and offered two four-year courses. In 1851, a new three-story county courthouse in the Greek Revival style was constructed, built from brick manufactured at Cobb's Hill by Gideon Cobb, at a cost of $76,000.

Abolition movement Rochester was the home for many years of abolitionist Frederick Douglass, a formerly enslaved African American who in 1847 began publishing an abolitionist newspaper, The North Star, in Rochester. Other prominent abolitionists in Rochester included Amy and Isaac Post and Abigail Bush.