Black History Month became situated within Febuary because of famous abolitionist and publisher Fredrick Douglass.
Like most people born into slavery, Douglass never knew his birthday, so he invented one. Because he knew he was born in the teens, he chose 1817 as his birth year. Douglass also recalled his mother calling him her "little valentine," so he chose February 14 as his birth date.
In 1926, a man named Dr. Carter G. Woodson founded Negro History Week-- which later was extended into Black History Month in 1976-- he chose the second week of February in Douglass' honor.