Co rich Hf-Co alloys demonstrate promising properties as potential permanent magnet systems. However their structure has not been well established by experiment. We performed a search for low-energy structures of the HfCo7 system with recently developed adaptive genetic algorithm. Among the low-energy structures with 16 and 32 atoms per unit cell, we found structural motifs similar to the permanent magnet SmCo5. For the unit cell size larger than 40 atoms, we found a phase separation into pure hcp Co and Hf2Co7 in agreement with the experiment. Calculated magnetization and temperature of magnetic phase transition are similar to those for hcp Co. Overall considered HfCo7 system represents a mix of in- and out-of-plane magnetic anisotropies systems with possible site dependence of magnetic anisotropy.