Each signer of any initiative or referendum petition must be a qualified elector of the state. He shall place on such petition after his name the date of signing and the location of his voting residence, including the street and number in which such voting residence is located, if in a municipal corporation, and the rural route or other post-office address and township in which such voting residence is located, if outside a municipal corporation. Each signer may also print his name so as to clearly identify his signature. Each part-petition which is filed shall contain signatures of electors of only one county. Petitions containing signatures of electors of more than one county shall not thereby be declared invalid. In case petitions containing signatures of electors of more than one county are filed, the secretary of state shall determine the county from which the majority of signatures came, and only signatures from such county shall be counted. Signatures from any other county shall be invalid.