Hi, I noticed your query and looked it up while at the library today. Here is an excerpt from the following book:
Title: "A History of Indian River County" Author: JOHNSTON, Sidney P. Copyright year: 2000 Publisher: Indian River County Historical Society Place: 2636 14th Ave. Vero Beach, Florida 32961
Excerpt is as follows on page 14; Changing County Names Upon taking charge of the new Territory of Florida in 1821, Governor Andrew Jackson created two counties governing his jurisdiction. St Johns County embraced all of the peninsula east of the Suwanne River. For the next century, Florida continued to be subdivided into increasingly smaller county jurisdictions, ending with 67 counties in 1925. Two counties whose names have disappeared. Mosquito and Santa Lucia, once governed activities in present-day Indian River County. The name Mosquito County stuck until 1845, when the Legislature discarded it as discouraging to new settlement. Santa Lucia County, organized in 1844, took its name from the temporary for that the Spaniards set up near Jupiter Inlet in 1855 and resurrected as St. Lucie County in 1905. St Lucie, the matron saint of Syracuse, Italy, inspired the name. In all, Indian River County fell within five earlier jurisdictions: St Johns County (1821-1824); Mosquito County (1824-1844); Santa Lucia county (1844-1855); Brevard County (1855-1905); and St. Lucie County (1905-1925).
I know this is lengthy, but I wanted to give you details and documentation. I have a copy of the page I transcribed to you. I hope this helps you on your search. R.S.V.P. so I know you received this reply. Thank you. Linda