Rev. William Henry Jernagin (October 13, 1869 – February 18, 1958) was an African-American Baptist pastor, an important figure in the civil rights movement (1896–1954), and Pan-African activist. The National Race Congress selected Jernagin to attend the Paris Peace Conference and the First Pan-African Congress in 1919.

William Henry Jernagin was born in Mashulaville, Mississippi, on October 13, 1869, to Allen Fletcher Jernagin and Julia Ruth Walker. While his parents were mostly illiterate, they managed to obtain a small 40-acre farm upon which they grew a variety of fruits and vegetables. His family worked primarily harvesting apples and peaches for Juke Jernagin, a former slave owner. In the breaks between the sowing and reaping seasons, William attended a number of public schools in the Noxubee and Lauderdale Counties, among them Meridian Academy, Alcorn A&M College (now Alcorn State University), and Jackson College. In addition, he attended American Correspondence School located in Danville, N.Y.

After working in a school in Lauderdale County for roughly five years, Jernagin was licensed to preach by the Bush Fork Baptist Church of Mississippi. In 1892, two years after his pastoral licensing, the 23-year-old Jernagin was called to preach at a number of Mississippi Baptist Churches including: New Prospect Baptist Church in Meridian, Mississippi, Mount Moriah Baptist Church, and Scooba Baptist Church in Okolona, Mississippi.

The year of 1896 was a busy one for Jernagin, who worked to unite a number of churches, among them: Missionary Union Baptist Church, First Baptist Church in Winona, Mississippi, Second Baptist Church, First Baptist Church in Mound Bayou, Mississippi, First Baptist Church in Brandon, Mississippi, and Tabernacle Baptist Church in Oklahoma City, Oklahoma. During this year, he founded Mississippi's Meridian Baptist Seminary, which was among the first educational institutions for African Americans east of the Mississippi River and helped establish an educational standard for African-American Baptist pastors. In addition, he became the president of the Oklahoma General Baptist Convention, aided in the establishment of the Winona-Granada Baptist College, and organized the Young People's Christian Educational Congress of Mississippi.

In 1905, following his rapid string of accomplishments for the church and well-received pastorates all across the state of Mississippi, Jernagin was appointed to the Tabernacle Baptist Church, which led him to move to Oklahoma City, Oklahoma. An article run by the Oklahoma Safeguard on July 6, 1905, stated of the young pastor: "The installation of Reverend W.H. Jernagin as pastor of the Tabernacle Baptist Church, of Oklahoma City was pulled off last Sunday in good shape. Rev. Jernagin, seated away back in that fine church, confronted with an audience of from five hundred to eight hundred, surrounded by all the big preachers, lawyers, doctors, teachers and big men of that great city, looked as though he was old Pope Leo."

He served as Tabernacle's pastor for nine years and used his position in the community and personal influence within the National Baptist Convention (NBC) to engage a number of statewide and nationwide problems relating to Jim Crow policies. With the aid of others, Jernagin formed the State Constitutional League of Oklahoma whose expressed goal was to "secure the manhood rights of the race [sic] in concert with rights anticipated by other Americans". Jernagin himself testified in court advocating against the admission of the Oklahoma territory and Indian territory into the United States, decrying the idea as a move that would further entrench Jim Crow laws. William Harrison, a local attorney based out of Oklahoma City, aided the State Constitutional League in bringing a suit before the United States Supreme Court. A key feature of the case involved the Interstate Passenger Law. "Harrison knew [that the] success [of the case] would put an end to all 'Jim Crowism' as far as interstate passengers were concerned."

In 1912, Reverend Jernagin was appointed to serve in Washington, D.C., at the Mount Carmel Baptist Church. While this move marked the end of his residence in the state of Oklahoma, his influence in the state's affairs certainly never abated. On November 16, 1912, The Washington Bee, a prominent African-American weekly newspaper based in Washington, D.C., said of his installation and ensuing pastorate: "[Jernagin] is a wide-awake man. He is an eloquent and logical speaker, and his people think the world of him. [ ... ] there has never been a man at this church who has ever been more honored and respected than [Jernagin] ... it is quite evident ... that his administration will be a success". He would go on to serve the Mount Carmel congregation and the broader D.C. community with distinction for an illustrious 46-year term until his death in 1958.

During his first few years of serving in the nation's capital, Jernagin's position and clout within the National Baptist Convention continued to increase. Additionally, his influence in the surrounding communities steadily rose as he expanded his social networks to include key individuals, most notably: The Washington Bee publisher William Calvin Chase, activist and newspaper editor William Monroe Trotter, fellow Baptist, Reverend Walter Henderson Brooks, educator and founder of the National Training School for Women and Girls Nannie Helen Burroughs, and clubwoman Mary Church Terrell. These individuals supported Jernagin, effectively and efficiently "incorporating him into the organizations and issues that advocated for civil and human rights", while also providing him a myriad of sociopolitical avenues to approach the racial and religious issues he sought to engage with.