BAR HARBOR, Maine — Monday was just another day for Marisa Gray, 17, taking the Island Explorer bus to her job at the Hannaford grocery store in Bar Harbor.

Not for the Friends of Acadia National Park, however. When Gray stepped off the bus next to the village green, the organization proclaimed Gray to be passenger No. 5 million for the bus service that ferries people throughout the park and Mount Desert Island.

Gray, apprised of her minor celebrity status by the organization at an earlier bus stop, was interviewed by reporters after remarks by a handful of officials. She also received a goody bag with gifts.

Gray, who will be a junior at Mount Desert Island High School, lives in nearby Otter Creek with her family, having relocated from Texas in 2013. She has been working for a few months at the grocery store, bagging groceries and retrieving shopping carts.

The Island Explorer now serves roughly 500,000 passengers a year, about 20 percent of whom are local residents, according to Stephanie Clement, conservation director for Friends of Acadia. Clement identified Gray as passenger No. 5 million at an earlier stop and “gave her the good news,” she said.

The seasonal bus system, in its 16th year, does not charge for rides. David MacDonald, president of Friends of Acadia, noted that the buses help alleviate traffic in the region, which is a magnet for summer tourists and residents. “Each day they take thousands of cars off the road,” he said.

A member of a New Jersey family was proclaimed the 4 millionth passenger in 2011.

The bus service operates on eight routes that link hotels, inns, and campgrounds with sites in Acadia National Park and neighboring villages. It provides free transportation to visitors and residents alike — aboard about 30 propane-powered buses — to hiking trails, carriage roads, and beaches in the park as well as village shops, restaurants, and other businesses.

The bus service had nearly 424,000 passengers last year, a figure that was lower than expected because of the federal government shutdown in October, which closed the park and resulted in some bus routes being halted and others being re-routed out of the park.

The Island Explorer is operated by Downeast Transportation, a nonprofit organization based in Trenton that also provides year-round transit bus services throughout Hancock County.

More than half the funding to operate the Island Explorer comes from transit fees that are part of the Acadia National Park weekly and annual entrance passes. The state Department of Transportation and federal Transit Administration provide the next largest contribution, followed by L.L. Bean, which provides $200,000 annually to Friends of Acadia for the bus system. Local municipal appropriations, fees from businesses that receive front door service, passenger donations, and other donations make up the rest of the operating budget.