"Mogi" or "Moji"
There is a controversial issue on spelling the city’s name, which is originally from Tupi m'boîjy (river of snakes). The issue can be summarized as orthographic vs. historical.
On the one hand, in Portuguese, grammatical rules dictate that names of Indian (that is, Tupi) origin should be spelled with "j". Thus renowned dictionaries such as Houaiss spell the word in this way, "moji." This spelling is followed by IBGE.
On the other hand, in all historical documents the city's name has been written with "g" since its foundation. The city is called "Mogi" by the city government, the state government, the railroad company, its two universities, and its dwellers, with very few exceptions.
In a Google test, the spelling "Mogi das Cruzes" outnumbers "Moji das Cruzes" by 15:1.
Read more about this topic: Mogi Das Cruzes