Larus lacus is an extinct species of gull that lived in North America during the Late Pliocene.
The genus name Larus derives from Ancient Greek, referring to a seabird. The species name lacus derives from Latin, meaning "lake or standing body of water, in reference to the lagoonal deposits at the type locality."
Larus lacus specimens stem from Sarasota County, Florida. The humerus of Larus lacus most closely resembles the Hartlaub's gull (Chroicocephalus hartlaubii), black-headed gull (Chroicocephalus ridibundus), brown-hooded gull (Chroicocephalus maculipennis), and Franklin's gull (Leucophaeus pipixcan).