In 1813 , the Congress of Chilpancingo had their first meeting . On 6 November of that year , the Congress signed the first official document of independence , known as the `` Solemn Act of the Declaration of Independence of Northern America '' . In 1818 , the Congress of Chilpancingo was convened and on 6 November of that year , the Congress signed the first official document of independence , known as the `` Solemn Act of the Declaration of Independence of Northern America '' .