Well, Jacksonville is the largest in the "lower 48" but Alaska has 4 that each of them make Jacksonville look like a small town...He had it backwards, I lived in Jax for a few years recently and Jax is in Duval county. But the county isn’t the biggest, Jacksonville is the biggest city in the US.
To the OP I just moved away from there. If offering Medicare products, have UHC, United American and Humana for Med supps.
For MAPD have uhc, Humana/Careplus, Aetna/Coventry.
For FE it’s just the usual players that you would normally have in your bag.
List of United States cities by area - Wikipedia