Eliza was under the command of the Viceroy of New Spain (now Mexico). The Viceroy’s full name was: Juan Vicente de Güemes Padilla Horcasitas y Aguayo, 2nd Count of Revillagigedo.
To honor the Viceroy, Eliza named the area around what is now Orcas Island “Horcasitas” and from that point on, the island was known as Horcasitas on Spanish maps.
The English, not satisfied with the Spanish version of names (or native names for that matter) eventually shortened the name to “Orcas” on their charts in 1847. The new, abbreviated name stuck and the island has been known as Orcas Island
This is why the name is such an interesting coincidence. The name of the island and the name of the whale appears to have no connection at all.
The southern resident orcas were probably swimming these waters when Orcas Island originally got its name. This begs the question: Were the whales named after the island? The short answer is no. Their name comes from their scientific classification as Orcinus Orca
(1758), which references a god of the underworld.
For most of their history, they were called blackfish or killer whales because they were seen killing much larger whales. Only in the 20th century did we start calling them orca whales. For the record, orca whales are technically large dolphins.