Mainers With Loon Plates Get Into State Parks Free Sunday Simply having loon license plates on your vehicle scores you free admission to many state parks in Maine this weekend. Mainers with valid loon conservation license plates on their vehicle can get into many state parks Sunday, July 18. According to the Maine Department of Agriculture, Conservation and Forestry, "free admission is a thank you to everyone who purchases this special plate! Maine Loon license plates support conservation efforts of both Maine's State Parks and the Department of Inland Fisheries and Wildlife." While most state parks are participating the following are not: