The National Parks Service’s Network to Freedom definition:

The Underground Railroad refers to the effort of enslaved African Americans to gain their freedom by escaping bondage.

Wherever slavery existed, there were efforts to escape, at first to maroon communities in remote or rugged terrain on the edge of settled areas. Their acts of self-emancipation made them "fugitives" according to the laws of the times, though in retrospect "freedom seeker" seems a more accurate description. While most freedom seekers began their journey unaided and many completed their self-emancipation without assistance, each decade in which slavery was legal in the United States saw an increase in active efforts to assist escape. (View full quote)

In many cases the decision to assist a freedom seeker may have been a spontaneous reaction as the opportunity presented itself. However, in some places, and particularly after the Fugitive Slave Act of 1850, the Underground Railroad was deliberate and organized. Despite the illegality of their actions, and with little regard for their own personal safety, people of all races, classes and genders participated in this widespread form of civil disobedience. Spanish territories to the south in Florida, British areas to the north in Canada, Mexico, the Caribbean, and other foreign countries offered additional destinations for freedom. Free African American communities in urban areas in both the South and the North were the destination of some freedom seekers.

World Book Encyclopedia:

Underground railroad was an informal system that helped slaves escape to the Northern States and Canada during the mid-1800's. The system was neither underground nor a railroad. It was called the Underground Railroad because of the swift, secret way in which the slaves escaped. The slaves traveled by whatever means they could, moving almost entirely at night and hiding during the day. The fugitives and the people who aided them used many railroad terms as code words. For example, hiding places were called stations, and people who helped the runaways were known as conductors.
The Underground Railroad had no formal organization. Free blacks and some whites in both the South and the North provided the runaways with food, clothing, directions, and places to hide. Some Southern slaves also helped fugitives escape. In the North, many Quakers and other white abolitionists furnished hiding places and helped slaves move from one refuge to the next.
The term Underground Railroad was first used about 1830. From then until 1860, the system helped thousands of slaves escape. Some settled in the North, but there they could be captured and returned to slavery. Therefore, many fled to Canada, especially after Congress passed a strict fugitive slave law in 1850. The major haven for runaways in Canada was southern Ontario

There are various other maps available to provide a visual on the movement across the country:Overview , More detailed

Historian Wilbur H. Siebert provided the most detailed map in his 1898 Book “The Underground Railroad From Slavery to Freedom. Routes on his map of Illinois are highlighted in red. View Siebert Map

Amateur Historian James Ransom, Sr. has also updated a map (1993) reflecting routes. See the publication “Historic Illinois” published by the Illinois Historic Preservation Agency, division of Preservation Services, Vol. 22, #6 dated April 2000.

“Hush, hush…somebody’s callin’ my name. Sounds Like Freedom…somebody’s callin”
Spiritual-