The Revolution devastated Westchester County. Seven years of raids and plundering left much of the countryside a waste. Many homes had been burned.

The population of the county was reduced by more than 1,000 through war casualties and the emigration of Loyalists to Canada and England.

The former Loyalists who remained were often the objects of bitter resentment.

In 1784 Bedford citizens voted at a town meeting that "no persons that have been over to the Enemy shall come to the town to reside. And if any have already come in, they are to be immediately Drove out" (Griffin, Westchester County and Its People).

 As Westchester began the task of rebuilding, there was one big change that benefited local farmers. Many of the landholdings in the county had belonged to Loyalists and were confiscated by the state and sold by the Commissioners of Forfeiture. In all, the Westchester holdings of fifty-four Loyalists were thus sold off; the largest of these was Philipsburgh Manor. As a result of such sales, many farmers were able to buy the lands they had previously farmed as tenants.

In 1788 the county was formally divided into twenty towns. The first federal census, taken in 1790, showed a Westchester population of 24,000, mostly concentrated in the northern part. The chief occupation was farming, and during the early part of the nineteenth century, subsistence farming was the rule. Crops included potatoes and other vegetables, fruit, corn, and wheat. Every farm had dairy cows and poultry, and sheep were grazed on land too rough for cultivation.

As New York City recovered from British occupation, Westchester farmers began to sell their cattle and produce there. Sing Sing (now Ossining), on the Hudson, and Sawpit (now Port Chester), on the Sound, were the main ports to which farmers delivered their crops for shipment to New York. Cattle were driven directly to city markets on the hoof.  

Improved roads were a necessity for getting both cattle and crops to market. In 1800 the first commercial toll road, the Westchester Turnpike, was chartered, running through Pelham and New Rochelle. Toll gates were erected at intervals, and the charge was four cents for a horse and rider, ten cents for a one-horse passenger vehicle, and twenty cents for a stagecoach. In the northern part of the county, the Croton Turnpike (also called the Somerstown Turnpike) linked Somers to the Hudson River at Sing Sing. The turnpikes were made free public roads by the middle of the nineteenth century.

In addition to the turnpikes, the Albany, Danbury and Boston post roads were used to convey produce to market, as well as to carry the mail. These roads were also the main routes for stagecoach travel. Taverns and inns did a brisk business along these main roads. Taverns also often served as post offices. For example, the Ward house in Eastchester was both tavern and post office after the Revolution.

Despite the gradual improvement of the roads, travel by water remained the most practical and convenient way to get both passengers and freight to New York. Sloops made regular stops at the docks of the towns along the Hudson. Steamboats began to ply the river after Robert Fulton's Clermont made its first Hudson trip in 1807. The steamboats, however, landed on the west side of the Hudson; Westchester passengers had to be rowed out to board them. Sloops and steamboats shared the water transport business for many years on both the Hudson and the Sound.

As the economy of the new nation began to expand, small industries developed in Westchester. Cottage industries, chiefly shoemaking, had been prevalent before the Revolution, providing farming families with a small but welcome cash income. After the war these occupations began to be carried on in "factories." The work was still largely done by hand, but in buildings, often barns, specifically devoted to that purpose.

Only gradually were larger industries established. Iron foundries in Port Chester, Peekskill, and Morrisania (now part of the Bronx) made stoves and plowshares. Brickyards grew up in Croton and Verplanck. Marble quarries in Tuckahoe, Sing Sing, Hastings, and Thornwood supplied the nation with the building material necessary for the neoclassic architecture so popular in the nation's public buildings. For instance, many federal buildings destroyed by the British during the War of 1812 were rebuilt with Westchester marble. The local marble quarries were the main reason that New York State chose Sing Sing as the site of a new prison, begun in 1825.

The Croton Dam
Two developments in the 1830s and 1840s had an enormous effect on Westchester's growth. The first was the construction of the Croton Dam and Aqueduct, and the second was the building of the railroads. New York City's importance in the history of Westchester County is nowhere more apparent than in the watershed construction that began in the 1830s. The Croton River was determined to be the best source of water for the rapidly growing metropolis, and despite the misgivings of many local residents, the first Croton Dam was begun in 1837 and completed in 1842. 

The railroads came in the 1840s. By the summer of 1842, the New York and Harlem Railroad was running trains as far as Williamsbridge, and by 1844 the railroad had reached White Plains. The New York and Hudson River Railroad was being constructed in the same period and reached Peekskill in 1849. On the east side of the county, the New York, New Haven and Hartford opened its line in 1849. Both the railroads and the New York City water system were constructed chiefly by Irish laborers, who were emigrating in large numbers during this period to escape the famine in their native land.

One of the effects of rail service in Westchester was the shift from subsistence farming to dairying. Many farms began producing milk commercially once the railroads were available to make daily "milk runs".

The coming of the railroads brought a shift in population from the northern part of the county to the southern. Before the railroads, the most populous town in Westchester was Bedford. Between 1845 and 1855, the population of the county increased by 33,000, with most of the people choosing to live in the towns close to the railroad lines. The area of Eastchester that became Mount Vernon was hardly settled at all before 1850. In that year John Stevens of New York organized the Industrial Home Association No. 1, bought 367 acres of farmland in Eastchester, and laid out streets and building lots for a new town. This type of development was to be repeated in other sections of Westchester. By 1860 the total population of the county was 99,000, and Yonkers was the largest city.  

Social life in Westchester during the first half of the nineteenth century revolved very much around church, school, and home. While churches after the Revolution were no longer involved in politics, they remained centers of community life. New churches were built and old ones rebuilt. Evangelical meetings like the Methodist Camp Meeting, established in 1834 at Sing Sing, were enormously popular.  

Public schools were first established in Westchester County through an act of the New York legislature in 1795. A later act, in 1812, established the State Superintendent of Common Schools, thus creating the first state system of education in the country. Westchester's public schools in the nineteenth century were generally small, one-room affairs, but private schools also began to flourish early in the century. Notable examples were the North Salem and Bedford academies, and the Mount Pleasant Military Academy in Ossining.  

While most Westchester citizens were hard-working farmers and small businessmen, there was a scattering of wealthy and nationally known residents. John Jay and his descendants lived in Katonah. Washington Irving built Sunnyside on the Hudson River at Tarry-town. Artists such as Robert Havell, Jr., chose the Hudson River area for their homes and shared its beauty with the world through their paintings.  

The Civil War had a great effect on Westchester even though fighting never touched county soil. At the outbreak of the war, many residents had mixed feelings about the strong anti-slavery stand of Lincoln and the Republicans. Lincoln did not carry the county in 1860 or 1864.  

After the Southern states seceded, however, sentiment shifted toward solid support for the Union. Many young Westchester men volunteered. Once the initial enthusiasm wore off and there were fewer volunteers, towns began to offer bounties to entice men to sign up. This system was not successful, however, so in March 1863 a draft law was enacted. Draft rioters in New York moved up into Westchester but were persuaded to disband.

Throughout the war, Westchester citizens contributed what they could to the war effort. Church bells rang out in every town for each Union victory, and people gathered in the churches for public readings of the few available newspapers. Ladies' groups sewed clothing and made bandages to send to the soldiers in the field.

The end of the war brought problems created by the readjustment of returning soldiers, a greatly increased cost of living, and a slower growth in population. The more industrial southern part of Westchester grew faster than ever, however, and the county was soon ready to begin a new era of prosperity.