Johann Koehnken (born September 14, 1819 – 1897) was an American organ builder in Cincinnati, Ohio who worked under Matthias Schwab (1808-1862) and with Gallus Grimm (1827-1897). Their organs remain in use (with restoration work) at the Isaac M. Wise Temple (formerly Plum Street Temple) and other locations.
Much of Matthias Schwab's personal life remains a mystery. He arrived in Cincinnati in 1831 and in 1860 he apparently relinquished ownership of his factory at Sycamore and Schiller to Johann Heinrich Koehnken who was assisted by Gallus Grimm.
Koehnken was born on a farm in Altenbuhlstedt in the Lower Saxony area of Germany (not far from Bremen) and was apprenticed to a cabinetmaker. He worked as a cabinet maker for two years in Germany and two more in Wheeling before coming to Cincinnati in 1839. He "found his way to the door of Matthias Schwab", who had trained as an organ builder in Germany and operated a "highly regarded organ works in the fast-growing river town of Cincinnati." 
When Schwab retired in 1860, Koehnken and Grimm, a German-trained organ builder, continued the tradition and the firm became Koehnken and Company. Grimm partnered with Koehnken from 1875 and the firm became Koehnken & Grimm. They worked together for twenty-one years until Koehnken retired in 1896. In 1897 both Koehnken and Grimm died.
- St. John Lutheran Church in Chehalis, Washington has a Koehnken and Grimm organ from 1895. It was relocated from St. Mary's Catholic Church in Shawnee, Ohio before that building was demolished.
- St. John's United Church of Christ in Madison, Indiana 
- Isaac M. Wise Temple (formerly Plum Street Temple) in Cincinnati, Ohio has a Koehnken organ.
- Holy Family Catholic Church. It was relocated from Our Lady of Perpetual Help in Sedamsville to Holy Family in Price Hill.
John Rimmer inherited the business?
- CD157 Thom Miles at Plum Street Temple, Cincinnati Arsis Audio
- Orpha Caroline Ochse The History of the Organ in the United States page 296
- "the minister, August Meuller, and a committee went to Cincinnati and bought a Koehnken & Grimm organ with a hand pump for $1,000.00; it was put in operation just prior to Easter services in 1879. It replaced a "parlor pump organ" they had purchased in 1851 for $300.00. This was more likely a small pipe organ, but of it no more is known. The Koehnken & Grimm was originally hand-pumped and later equipped with a water motor (note photograph of the water valve above). Since the 1940s it has had a electric blower. At some point the swell shutters were relocated to the back of the swell box, and a solid plywood wall now fills the old opening, making the organ much softer than its builders intended." Organ history (Alan Miller Laufman, 1993 Organ Historical Society Handbook) Southern Indiana chapter of the American Guild Organists (Includes photos and sound samples)