Cockeysville is a census-designated place (CDP) in Baltimore County, Maryland, United States. The population was 20,776 at the 2010 census.

The low-lying valleys in and around Cockeysville are underlain by a soft, crystalline metamorphic rock called Cockeysville Marble. This rock, which was once limestone at the bottom of an ancient sea, erodes much faster than the surrounding harder schist. This process created fertile, rolling valleys with rich, lime-sweetened soils. These valleys supported mature hardwood forests. Dominant tree species would have included tulip poplar, American chestnut, various oaks (white, red, black), hickories, black walnut, and American elm. The understory would have had flowering shrubs and herbaceous plants like pawpaw, spicebush, mayapple, Virginia bluebells, and various ferns. Large mammals such as white-tailed deer, elk, and black bears were abundant. The area was also home to predators like mountain lions and bobcats. Smaller mammals included beavers, river otters, gray foxes, and woodland bison. There were wild turkeys, passenger pigeons, barred owls, and numerous songbirds.

In contrast to the fertile valleys are the nearby serpentine barrens, such as Soldiers Delight Natural Environmental Area. These ecosystems are formed on serpentinite, a greenish metamorphic rock low in essential plant nutrients like calcium and high in heavy metals like magnesium, nickel, and chromium, which are toxic to most plants. These areas included prairie grasses like little bluestem, pitch pine, scrub and post oaks, and eastern redcedar. Grasslands attracted grazing animals like elk and white-tailed deer. The habitat also supported specialized insects, including unique moths and butterflies. Birds of the open country, such as bobwhite quail and field sparrows, would have been common.

The dominant Native American group in this part of Maryland was the Iroquoian-speaking Susquehannock tribe. They cultivated large fields of the "three sisters" along rivers and streams. They hunted deer, elk, bear, and turkey for meat and hides. They also foraged for nuts (hickory nuts, walnuts, chestnuts), berries, and edible plants. By the late 17th century, a combination of diseases introduced by Europeans and prolonged warfare with the neighboring Iroquois Confederacy reduced the Susquehannock population. European settlers came into a largely depopulated wilderness with lush natural resources.

The Cockey family were prominent landowners and influential figures in Baltimore County. Thomas Cockey (1676–1737) settled in the Limestone Valley region in 1725 at Taylor's Hall (an area now just north of Padonia Road and east of I-83).

Cockeyville's founding is usually credited to Joshua Frederick Cockey (1765–1821), who in 1810 opened a hotel and tavern at a central junction on the Baltimore and York-Town Turnpike (York Road), a major toll road chartered in 1787 that served as the primary route for horse-drawn wagons and stagecoaches moving between the port of Baltimore and points north into Pennsylvania. Cockey's hotel became a stopping point for travelers, teamsters, and farmers, and a small commercial center soon grew up around it.

In the 1830s, the Baltimore and Susquehanna Railroad (later the Northern Central Railway) laid tracks through the village, paralleling the York Road. Cockeysville was now a station on a rail line connecting Baltimore to Harrisburg and the national rail network. The dual-transportation hub made the village a commercial hub for northern Baltimore County. The railroad allowed the export of marble from the nearby Texas and Beaver Dam quarries; limestone, and agricultural products like grain, hay, and dairy were sent by freight car. The town grew, a post office was established, churches founded, and new businesses serving the surrounding agricultural and industrial community. Judge Joshua F. Cockey (1800–1891), a lifelong resident who was a businessman before being appointed as judge in the 1830s, built the town train station and accompanying commercial buildings. In 1851, Cockeysville citizens voted against becoming the county seat. The town wanted to retain its rural character, and was concerned about a county jail that could instigate disorderly gatherings. The county seat went instead to Towson, Maryland.

Cockeysville was the scene of some Civil War activity. Confederate soldiers pushed into the Baltimore area, intending to cut off the city and Washington from the north. On July 10, 1864, Confederate cavalry under General Bradley T. Johnson entered Cockeysville, destroying telegraph lines and track along the Northern Central Railway. They also burned the first bridge over the Gunpowder Falls, just beyond nearby Ashland. Abraham Lincoln passed through by train several times, including on his way to give the Gettysburg Address and when his funeral train's return to Illinois. After the war, Joshua F. Cockey III (1837–1920) founded the National Bank of Cockeysville (1891) and other commercial ventures in the community, as well as developing dwellings along the York Turnpike.