Vacation Rental Investment Across the Other Casco Bay Islands: Real Demand, a Real Housing Tension, and Rules Nobody Has Confirmed Yet

Real Seasonal Demand -- and the Housing Tension It Creates

Every one of these five islands shows a dramatic gap between its year-round population and its summer population, and that gap is real, sourced evidence of strong seasonal demand for property here. Long Island's year-round population was 234 at the 2020 Census, with a summer population that swells to roughly 800 to 1,000 -- more than triple. Chebeague Island's year-round population was 396 at the 2020 Census, and Casco Bay Lines' own island page describes a summer population of more than 1,600 against just over 360 year-round residents -- again, more than a fourfold seasonal increase. Cliff Island runs a similar pattern, roughly 60 year-round residents swelling to about 200 in summer. That multiple, repeated across three of these five islands with independent sourcing, is genuine evidence that people want to be here seasonally, not just as day-trippers.

But a July 2025 Portland Press Herald investigation into housing shortages on Maine's unbridged islands -- explicitly naming Chebeague, Long Island, Peaks, and Cliff Island among the Casco Bay islands it examined -- found that this same seasonal-demand pattern is a documented driver of an island-wide housing-affordability crisis. Wealthy outside buyers converting year-round homes into seasonal-use property was identified as a real factor pushing up housing costs, alongside island construction costs running roughly 30% higher than mainland costs (driven by barge transport and infrastructure needs) and a limited land supply constrained by conservation easements. The same investigation found the median island resident is 56 years old, against 44 statewide. In other words, the exact demand pattern that makes a vacation-rental or seasonal-retreat purchase here plausible is the same pattern year-round island residents and their own housing advocates are actively working against.

Chebeague Island's own response effort is genuinely documented and worth naming directly: the Chebeague Island Community Association (CICA) has run real affordable-housing projects for more than a decade, including a modular duplex at 43 School House Road, built with a $350,000 MaineHousing grant and installed in May 2012 (occupied by two island families by that fall); a 2013-2014 rent-with-option-to-purchase house at 226 South Road; and a second modular duplex at 553 South Road, on land donated by Stacie and Toby Webb, built with Dirigo Homes and installed in May 2025, with tenants expected to move in during fall 2026. More broadly, MaineHousing's Affordable Housing Initiative for Maine Islands has funded 49 units across 10 islands, with grants up to $840,000 per project, and other islands in the broader investigation are trying modular construction and converting single-family homes into multi-unit rentals as additional responses. Anyone weighing a seasonal or short-term-rental purchase on Chebeague or Long Island should understand that a real local housing conversation is already underway about exactly this dynamic, not treat it as a footnote.

Diamond Cove: The One Genuinely Purpose-Built Vacation Community Here

If any single property on these five islands looks like a traditional vacation-rental-friendly product, it is Diamond Cove on Great Diamond Island -- and its story is worth understanding rather than assuming. Great Diamond Island was the site of Fort McKinley, a major coastal-defense installation built roughly 1897-1906, eventually covering 111 acres with nine gun batteries, and closed by the Army in 1947. The Navy sold the site to private interests in 1961, and the former army barracks and officers' quarters were converted into homes; the Fort McKinley Historic District was listed on the National Register of Historic Places in 1985. Diamond Cove today is a gated, mostly private residential community built out of that conversion, with its own on-site, public-facing businesses: Diamond's Edge Restaurant & Marina and the Diamond Cove General Store, plus the Inn at Diamond Cove.

That combination -- a gated community with its own restaurant, marina, general store, and inn, built specifically around seasonal residential and vacation use rather than year-round working-island life -- makes Diamond Cove structurally different from the other four islands in this group. It is the closest thing to a traditional resort-community product among these five, and it should be evaluated as its own micro-market, likely governed by its own HOA rules on top of whatever City of Portland short-term-rental ordinance may apply (Great Diamond Island has always been part of the City of Portland, never its own town). A specific current Zillow typical-home-value figure for Great Diamond Island or Diamond Cove could not be independently confirmed in the research behind this page, despite Zillow maintaining dedicated listing pages for both -- treat any such figure you encounter elsewhere as unverified until checked directly.

Little Diamond, Long Island, Chebeague, and Cliff Island: Four Very Different Rental Realities

Little Diamond Island already functions almost entirely as a seasonal and vacation retreat rather than a year-round neighborhood -- it had just 5 year-round residents at the 2000 Census, a figure explicitly attributed to the island's water supply being shut off in winter, and a more recent commercial demographics snapshot shows as few as 2 residents and 1 occupied household out of only 3 total housing units on the entire island. That near-total seasonal character might sound like a natural fit for vacation-rental investment, but the honest read is the opposite: an island this thin has essentially no dining, no store, and no visible rental-support infrastructure of any kind. A property here would be operating in genuine isolation from services, not inside a built-out vacation economy.

Long Island and Chebeague Island sit at the other end of the spectrum -- real, functioning year-round communities (each with its own elementary school and its own municipal government, having seceded from Portland in 1993 and from Cumberland in 2007, respectively) that also carry real seasonal populations several times their year-round base. Real estate data for both is a genuine reason for a prospective investor to pause rather than assume automatic appreciation: Chebeague's Zillow typical-home-value figure is $666,975, down 1.8% over the past year as of data through June 30, 2026, and Long Island's is $609,323, down 4.2% over the past year as of data through January 31, 2026. Both islands are showing recent price softening, not appreciation -- worth stating plainly rather than glossing over in a pitch for seasonal-property demand.

Cliff Island is the most remote of the five and the least resort-like: the longest Casco Bay Lines run in the group (commonly cited at roughly 60 to 120 minutes one-way), entirely unpaved roads, and a genuine year-round civic culture built around a one-room schoolhouse, a 100-plus-year-old library, and an all-volunteer community organization. Its dining roster is a single seasonal store and cafe. No reliable current median-sale or typical-home-value figure for Cliff Island (or for Little Diamond Island) was independently confirmed in the research behind this page -- both are thin, low-transaction-volume micro-markets where a single-digit number of annual sales can make any "median" figure statistically meaningless, and no number is invented here to fill that gap.

Ferry Dependency: A Structural Constraint No Mainland Market Has

Every guest arriving at a short-term rental on any of these five islands arrives by Casco Bay Lines ferry (Chebeague also has a second, separate operator, the Chebeague Transportation Company, running a shorter route from Cousins Island in Yarmouth). That is a genuine structural constraint a mainland coastal rental simply does not have: guest arrival and departure times are fixed by a published ferry schedule, freight and vehicle space is separately constrained and often reservation-only, and Cliff Island's own run can take up to two hours each way. A late guest, a missed boat, or a schedule change during a storm is a real logistics problem here in a way it is not for a rental a guest can simply drive to.

That constraint is not just theoretical right now -- it is live. In 2026, the Casco Bay Island Transit District proposed raising peak-season round-trip adult passenger fares from $14 to $17 (a 21% increase), with 30-day passes rising from $48 to $51 and off-peak daily fares from $7.20 to $8, citing rising fuel, labor, maintenance, insurance, and regulatory costs. It was the second passenger fare increase in three years, following a 2024 increase (the first in 15 years) and a separate 2025 vehicle-fare increase. Island residents filed a formal petition citing both affordability concerns and improper public notice, and on June 16, 2026, the Maine Public Utilities Commission unanimously voted to open a full, formal adjudicatory investigation into both the financial justification for the increases and the rate-setting process itself. As of that vote, the new fares remained in effect for the summer season while the investigation proceeded.

Separately, and worth noting because the numbers do not perfectly match the proposal coverage above, Casco Bay Lines' own current rates page lists a peak-season (April 18 through October 12, 2026) round-trip adult fare of $16.00 and an off-peak-season (October 13, 2026 through April 16, 2027) round-trip adult fare of $8.00 -- flat rates applied identically across all seven stops it serves, meaning the roughly two-hour round trip to Cliff Island costs a rider the same as the short hop to Peaks Island. Treat the carrier's own current rates page as the more authoritative, up-to-date figure, and re-verify directly with Casco Bay Lines before budgeting guest-transportation costs into any rental pro forma -- both the fare level and the outcome of the PUC investigation could change.

No Short-Term-Rental Ordinance Has Been Confirmed for Any of These Islands -- Verify Directly

No short-term-rental-specific ordinance, permit requirement, occupancy cap, or fee schedule for Long Island, Chebeague Island, Great Diamond Island, Little Diamond Island, or Cliff Island was independently confirmed in the research behind this page. That is stated plainly rather than filled in with a guess, because getting this wrong is exactly the kind of mistake that turns a promising purchase into a legal problem. Long Island and Chebeague Island are each their own incorporated town, with their own town government and (presumably) their own zoning and rental rules -- anyone considering a purchase there needs to check directly with the Town of Long Island or the Town of Chebeague Island. Great Diamond Island, Little Diamond Island, and Cliff Island are all part of the City of Portland (none of the three has ever been a separate town), so any short-term-rental ordinance governing them would run through Portland's own municipal government, not a separate island authority -- check directly with the City of Portland's planning department or code enforcement office before assuming a property on any of those three islands can legally be rented short-term.

Diamond Cove on Great Diamond Island adds a further layer worth flagging: as a gated, HOA-style community built out of the former Fort McKinley, it plausibly carries its own community rules on top of whatever the City of Portland requires -- another reason to verify directly rather than assume a Portland-wide answer automatically covers a Diamond Cove property.

What This Means Before You Decide

Put together, honestly: seasonal demand across these five islands is real and documented -- the summer-population multiples on Long Island, Chebeague, and Cliff Island, and the built-for-it character of Diamond Cove on Great Diamond Island, are genuine reasons a seasonal-rental thesis has something to stand on here. But that same demand is also a documented contributor to a real, currently-being-addressed island housing-affordability crisis, real estate on Chebeague and Long Island has recently softened in price rather than appreciated, Little Diamond and Cliff Island are thin enough markets that no reliable price figure exists for either, and every one of these islands runs entirely on a ferry system that is itself in the middle of a live fare dispute and a formal state investigation. None of that is a reason to avoid these islands -- it is the honest, structural picture a purchase decision here should actually rest on.

No specific nightly rate, occupancy percentage, booking volume, or short-term-rental permit fee for any of these five islands is stated on this page, because none was independently confirmed. Before committing to any purchase or renovation planned around short-term-rental income, verify current short-term-rental rules directly with the Town of Long Island or the Town of Chebeague Island (for those two islands) or the City of Portland (for Great Diamond, Little Diamond, and Cliff Island), and consult a qualified local real estate professional, accountant, and attorney about your specific situation. Nothing on this page is investment, legal, or tax advice.