Because the Fugitive Slave Law had made the northern United States more dangerous for escaped slaves, many began migrating further north to Canada. In December 1851, Tubman guided an unidentified group of eleven fugitives – possibly including the Bowleys and several others she had helped rescue earlier – northward. There is evidence to suggest that Tubman and her group stopped at the home of abolitionist and former slave Frederick Douglass. In his third autobiography, Douglass wrote: "On one occasion I had eleven fugitives at the same time under my roof, and it was necessary for them to remain with me until I could collect sufficient money to get them on to Canada. It was the largest number I ever had at any one time, and I had some difficulty in providing so many with food and shelter…." The number of travelers and the time of the visit make it likely that this was Tubman's group.
Harriet's third trip was in September 1851. She went to get her husband, John, but he had remarried and did not want to leave. So she went back up North. Harriet went to Garret's house and found there were more runaways (which were referred to as passengers) to rescue than anticipated. That did not stop her though. She gave a baby a sedative so he would not cry and took the passengers into Pennsylvania. The trip was long and cold but they did reach the safe house of Frederick Douglas. He kept them until he had collected enough money to get them to Canada. He recieved the money so she and her eleven passengers started the journey to Canada. To get into Canada, they had to cross over Niagara Falls on a handmade suspension bridge which would take them into the city of St. Catherine, Ontario in Canada. In St. Catherine, blacks and whites lived together in comfortable houses and they had their own land to farm and raise crops. St. Catherines remained her base of operations until 1857. While there she worked at various activities to save to finance her activities as a Conductor on the UGRR, and attended the Salem Chapel BME Church on Geneva Street.
Estimates vary widely, but at least 30,000 slaves, some saying 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, and Windsor. 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.