Estimates vary widely, but at least 30,000 slaves, and potentially more than 100,000, escaped to Canada via the Underground Railroad. The largest group settled in Upper Canada (called Canada West from 1841, and today Southern Ontario), where numerous Black Canadian communities developed. These were generally in the triangular region bounded by Toronto, Niagara Falls, andWindsor. Nearly 1,000 refugees settled in Toronto, and several rural villages made up mostly of ex-slaves were established in Kent County and Essex County.

Another important center of population was Nova Scotia, for example Africville and other villages near Halifax, see Black Nova Scotians. Important black settlements also developed in other parts of British North America (now parts of Canada). These included Lower Canada (present-day Quebec) and Vancouver Island, where Governor James Douglas encouraged black immigration because of his opposition to slavery and because he hoped a significant black community would form a bulwark against those who wished to unite the island with the United States.

Upon arriving at their destinations, many fugitives were disappointed. While the British colonies had no slavery after 1834, discrimination was still common. Many of the new arrivals had great difficulty finding jobs, in part because of mass European immigration at the time, and overt racism was common. For example, the charter of the city of Saint John, New Brunswick was amended in 1785 specifically to exclude blacks from practicing a trade, selling goods, fishing in the harbor, or becoming freemen; these provisions stood until 1870.

With the outbreak of the Civil War in the U. S., many black refugees enlisted in the Union Army and, while some later returned to Canada, many remained in the United States. Thousands of others returned to the American South after the war ended. The desire to reconnect with friends and family was strong, and most were hopeful about the changes emancipation and Reconstruction would bring.

To reduce the risk of infiltration, many people associated with the Underground Railroad knew only their part of the operation and not of the whole scheme. There were the "conductors" who ultimately moved the runaways from station to station. The "conductor" would sometimes pretend to be a slave to enter a plantation. Once a part of a plantation, the "conductor" would direct the runaways to the North. Slaves would travel at night, about 10–20 miles (15–30 km) to each station. They would stop at the so-called "stations" or "depots" during the day and rest. The stations were out of the way places like barns. While resting at one station, a message was sent to the next station to let the station master know the runaways were on their way.

The resting spots where the runaways could sleep and eat were given the code names "stations" and "depots" which were held by “station masters”. There were also those known as “stockholders” who gave money or supplies for assistance. Fugitives would refer to Canada as "The Promised Land" and the Mississippi River as "The River Jordan" as biblical references.

Although the fugitives sometimes traveled on boat or train,[15] they usually traveled on foot or by wagon in groups of 1–3 slaves. Some groups were considerably larger, however. Abolitionist Charles Turner Torrey and his colleagues rented horses and wagons and often transported as many as 15 or 20 slaves at a time.
Routes were often purposely indirect to confuse pursuers. Most escapes were by individuals or small groups; occasionally, there were mass escapes, such as with thePearl incident. The journey was often considered particularly difficult and dangerous for women or children, yet many still participated. In fact, one of the most famous and successful abductors (as people who secretly traveled into slave states to rescue those seeking freedom were called) was a woman, Harriet Tubman
Due to the risk of discovery, information about routes and safe havens was passed along by word of mouth. Southern newspapers of the day were often filled with pages of notices soliciting information about escaped slaves and offering sizable rewards for their capture and return. Federal marshals and professional bounty hunters known as slave catchers pursued fugitives as far as the Canadian border.
The risk was not limited solely to actual fugitives. Because strong, healthy blacks in their prime working and reproductive years were seen and treated as highly valuable commodities, it was not unusual for free blacks—both freedmen (former slaves) and those who had never been slaves—to be kidnapped and sold into slavery. 

Even at the height of the Underground Railroad, fewer than 1,000 slaves from all slave-holding states were able to escape each year (just over 5,000 court cases for escaped slaves recorded), a quantity much smaller than the natural annual increase of the enslaved population. Although the economic impact was small, the psychological impact on slaveholders of an informal network to assist escaped slaves was immense. Under the original Fugitive Slave Law of 1793, the responsibility for catching runaway slaves fell on officials of the states from which the slaves came, and the Underground Railroad thrived.

With heavy political lobbying, the Compromise of 1850, passed by Congress after the Mexican-American War, stipulated a more stringent Fugitive Slave Law. Ostensibly, the compromise redressed all regional problems. However, it coerced officials of free states to assist slave catchers if there were runaway slaves in the area, and granted slave catchers national immunity when in free states to do their job. Additionally, free blacks of the North could easily be forced into slavery, whether they had been freed earlier or had never been slaves. Suspected slaves were unable to defend themselves in court, and it was difficult to prove a free status. In a de facto bribe, judges were paid more ($10) for a decision that forced a suspected slave back into slavery than for a decision that the suspected slave was in fact free ($5). Thus, many Northerners who would have otherwise been able and content to ignore far-away regional slavery, chafed under nationally-sanctioned slavery. This led to one of the primary grievances of the Union cause in the Civil War.

The escape network was not literally underground nor a railroad. It was figuratively "underground" in the sense of being an underground resistance. It was known as a "railroad" by way of the use of rail terminology in the code. The Underground Railroad consisted of meeting points, secret routes, transportation, and safe houses, and assistance provided by abolitionist sympathizers. Individuals were often organized in small, independent groups; this helped to maintain secrecy because individuals knew some connecting "stations" along the route but knew few details of their immediate area. Escaped slaves would move north along the route from one way station to the next. "Conductors" on the railroad came from various backgrounds and included free-born blacks, white abolitionists, former slaves (either escaped or manumitted), and Native Americans. Churches also often played a role, especially the Religious Society of Friends (Quakers), Congregationalists, Wesleyans, andReformed Presbyterians as well as certain sects of mainstream denominations such as branches of the Methodist church and American Baptists. Without the presence and support of free black residents, there would have been almost no chance for fugitive slaves to pass into freedom unmolested.

Harriet Tubman (born Araminta Harriet Ross; 1820 – March 10, 1913) was an African-American abolitionist, humanitarian, and Union spy during the American Civil War. Born into slavery, Tubman escaped and subsequently made more than nineteen missions to rescue more than 300 slaves using the network of antislavery activists and safe houses known as the Underground Railroad. She later helped John Brown recruit men for his raid on Harpers Ferry, and in the post-war era struggled for women's suffrage.

Tubman and her brothers, Ben and Henry, escaped from slavery on September 17, 1849. Tubman had been hired out to Dr. Anthony Thompson, who owned a large plantation in an area called Poplar Neck in neighboring Caroline County; it is likely her brothers labored for Thompson as well. Because the slaves were hired out to another household, Eliza Brodess probably did not recognize their absence as an escape attempt for some time. Two weeks later, she posted a runaway notice in the Cambridge Democrat, offering a reward of up to 100 dollars for each slave returned. Once they had left, Tubman's brothers had second thoughts. Ben may have just become a father. The two men went back, forcing Tubman to return with them.

Soon afterward, Tubman escaped again, this time without her brothers. Beforehand, she tried to send word to her mother of her plans. She sang a coded song to Mary, a trusted fellow slave, that was a farewell. "I'll meet you in the morning," she intoned, "I'm bound for the promised land". While her exact route is unknown, Tubman made use of the network known as the Underground Railroad. This informal, but well-organized, system was composed of free and enslaved blacks, whiteabolitionists, and other activists. Most prominent among the latter in Maryland at the time were members of the Religious Society of Friends, often called Quakers. The Preston area near Poplar Neck in Caroline County contained a substantial Quaker community, and was probably an important first stop during Tubman's escape. From there, she probably took a common route for fleeing slaves - northeast along the Choptank River, through Delaware and then north intoPennsylvania. A journey of nearly 90 miles (145 kilometers), her traveling by foot would have taken between five days and three weeks.

Tubman had to travel by night, guided by the North Star, and trying to avoid slave catchers, eager to collect rewards for fugitive slaves. The "conductors" in the Underground Railroad used a variety of deceptions for protection. At one of the earliest stops, the lady of the house ordered Tubman to sweep the yard to make it appear as though she worked for the family. When night fell, the family hid her in a cart and took her to the next friendly house. Given her familiarity with the woods and marshes of the region, it is likely that Tubman hid in these locales during the day. Because the routes she followed were used by other fugitive slaves, Tubman did not speak about them until later in her life.

The Underground Railroad was a network of secret routes and safe houses used by 19th-century black slaves in the United States to escape to free states and Canada with the aid of abolitionists and allies who were sympathetic to their cause. The term is also applied to the abolitionists, both black and white, free and enslaved, who aided the fugitives. Various other routes led to Mexico or overseas. While an "underground railroad" running south toward Florida, then a Spanish possession, existed from the late 17th century until shortly after the American Revolution, the network now generally known as the Underground Railroad was formed in the early 19th century, and reached its height between 1850 and 1860. One estimate suggests that by 1850, 100,000 slaves had escaped via the "Railroad". British North America (present-day Canada), where slavery was prohibited, was a popular destination, as its long border gave many points of access. More than 30,000 people were said to have escaped there via the network during its 20-year peak period, although U.S. Census figures account for only 6,000.