Well in Chicago, it says that while originally Puerto Rican - Mexicans now rule the gang their by a vast majority. Something like 70 percent. As Chicago has a huge Mexican population apparently. Their group is known as King Motherland Chicago (KM/C) Or by the all-inclusive term Almightly Latin King Nation (ALKN). They are the ones who are usually the ones setting up chapters in other states or abroad.

In New York, the Latin Kings are a bit different IIRC.
They're a splinter faction called the "Bloodline". Founded by Luis Felipe, AKA King Blood. They also refer to themselves at the Almighty Latin King and Queen Nation (ALKQN) as a whole. I think he only had a marginal connection to the greater Latin King scene, before designating himself as Supreme Crown over the State of New York. The Bloodline is regarded by Motherland Latin Kings as not being true Latin Kings. Much Like the United Blood Nation (UBN) is a unsanctioned splitner group of the West Coast Bloods.

Bloodline Kings are mainly Puerto Rican, I think. Also some Dominicans and Columbians in the earlier days. It was reported tho that alot of Dominicans have dropped out to join the Trinitarios organization. Puerto Ricans in NY are known to have racial feuds with other Latinos. And apparently, Mexican Latin Kings are a rarity in NYC as well.

So all-in-all, Chicago Latin Kings are predominantly Mexican, plus any direct transnational chapters and sets. Bloodline or NYC Kings are mainly Puerto Rican. All claim to accept anyone tho. But because of cultural standards they end up taking in mostly Hispanics of Latin American descent.