There has been a renewed interest in zinc oxide in thematerials science community after it was shown to be ferromagneticwhen doped with cobalt. However, it has remained difficult to tellwhether the origin of the phenomenon was intrinsic or due tosecondary phases. Here, we examine with analytical transmissionelectron microscopy the distribution of cobalt in a thin film offerromagnetic Al-doped Zn0.7Co0.3O that we have grown bypulsed laser deposition on alumina. We show that precipitation ofa secondary phase does occur, but that it concerns less than 10%of the cobalt atoms. The precipitates appear to be made ofhexagonal metallic Co, and their average diameter is 4 nm. Theirmagnetism could be the reason for the low measured Curietemperature of the sample (50 K). On the other hand, the overallmeasured magnetization of 0.7 $\mu_B$ per cobalt atom suggeststhat the Co atoms in solution are at the origin of most of thesignal.