Hillsboro is a city in Marion County, Kansas, United States. Hillsboro was named after John Gillespie Hill, who homesteaded in the area in 1871. As of the 2020 census, the population of the city was 2,732. …Hillsboro is a city in Marion County, Kansas, United States. Hillsboro was named after John Gillespie Hill, who homesteaded in the area in 1871. As of the 2020 census, the population of the city was 2,732. Hillsboro is home of Tabor College, which had 766 students enrolled in Fall 2014.