He resumed his work with broad and elevated ideas of his business. This is clearly seen in the plan of his institution, embraced in the printed annual announcements and programmes of his annual exhibitions, copies of which have been preserved. The course of study embraced three years, and there was a male and a female department, Miss Catharine Costin at one period being in charge of the female department. Mr. Seaton, of the "National Intelligencer," among other leading and enlightened citizens and public men, used to visit his school from year to year, and watch its admirable working with deep and lively interest. Cook was at this period not only watching over his very large school, ranging from 100 to 150 or more pupils, but was active in the formation of the "First Colored Presbyterian Church of Washington," which was organized in November, 1841, by Rev. John C. Smith, D.D., and worshipped in this school-house. He was now also giving deep study to the preparation for the ministry, upon which, in fact, as a licentiate of the African Methodist Episcopal Church, he had already in some degree entered. At a regular meeting of "The presbytery of the District of Columbia," held in Alexandria, May 3, 1842, this church, now commonly called the Fifteenth Street Presbyterian Church, was formally received under the care of that presbytery, the first and still the only Colored Presbyterian church in the district. Mr. Cook was elected the first pastor July 13, 1843, and preached his trial sermon before ordination on the evening of that day in the Fourth Presbyterian Church (Dr. J. C. Smith's) in the city, in the presence of a large congregation. This sermon is remembered as a manly production, delivered with great dignity and force, and deeply imbued with the spirit of his work. He was ordained in the Fifteenth Street Church the next evening, and continued to serve the church with eminent success till his death in 1855. Rev. John C. Smith, D.D., who had preached his ordination sermon, and been his devoted friend and counsellor for nearly twenty years, preached his funeral sermon, selecting as his text, "There was a man sent from God whose name was John." There were present white as well as Colored clergymen of no less than five denominations, many of the oldest and most respectable citizens, and a vast concourse of all classes white and Colored. "The Fifteenth Street Church," in the words of Dr. Smith in relation to them and their first pastor, "is now a large and flourishing congregation of spiritually-minded people. They have been educated in the truth and the principles of our holy religion, and in the new, present state of things the men of this church are trusted, relied on as those who fear God and keep His commandments. The church is the monument to John F. Cook, the first pastor, who was faithful in all his house, a workman who labored night and day for years, and has entered into his reward. 'Blessed are the dead who die in the Lord.'