The organ of San Dionisio Ocotepec is one of Oaxaca's oldest, as confirmed by the date 1721 on a label inside the case. It was the first of the extant organs with religious figures painted on the case, a trend that continued throughout the 18th century. One wonders if this organ might represent a link to 17th–century organ building. Documents indicate that it was originally in the Tlacolula church and was sold to Ocotepec in 1792 to pay for the gilding of their new organ. The organist Juan Martinez, the founder of the Martínez family dynasty, would have played this organ in Tlacolula during the 1780s and would undoubtedly have been involved in the decision to sell it to Ocotepec. 

The doors of the organ, detached, framed, and hanging in the sacristry, depict the two religious figures associated with music: King David playing a harp and Saint Cecilia playing the organ of Tlacolula/Ocotepec as it once may have appeared with its bellows behind. Painted on the sides of the organ are images of sainted church scholars - Saint John Nepomuk on the right and an unidentified saint on the left - with their four-pointed black birettas and pectoral crosses; they carry palm fronds, symbols of their martyrdom. They are not Dominican saints since the Tlacolula church was secularized by this time. Cherubs are painted on either side near the base. The filler decoration on the case, details of the saints, and the decorated walls of the choir loft were touched up "authentically" in the 1990s.  

The lower case of the Ocotepec organ is narrower than the upper, and from then on, most stationary organs in Oaxaca were built with wider lower cases for stability. The drawstops (slider tabs) protrude from the sides of the case rather than the façade, even though the organ had suspended action and a substantial channel board to feed the façade pipes. During the IOHIO’s first visit in 2002, we were informed that the organ had nearly been thrown away the year before. The doors had fallen off and were on the floor; fortunately, they were retrieved and hung in the sacristy, and the case remained in the choir loft.