Ghon’s focus is found in
Ghon’s focus

In primary tuberculosis when inhaled tubercule bacilli implanted in the distal air spaces of the lower part of an upper lobe or upper part of the lower lobe, close to the pleura. This area is about 1 to 1.5 cm with caseating necrosis known as Ghon’s focus.
Ghon’s focus is one of the components of Ghon’s complex (primary complex), which consists of 3 components: -

i) Ghon’s focus (subpleural caseating lesion)
ii) Caseating hilar lymph node
iii) Draining lymphatics. 
Note - Due to early bacteremia (bacillemia) seeding of tubercle bacilli may occur at the apex to produce Simon’s focus.
Leprosy
Pulmonary tuberculosis
Sarcoidosis
Asbestosis