In O’Brien Homes, Inc. v. Lunenberg Planning Board (pdf), Land Court Judge Keith C. Long upheld a five-acre minimum lot size requirement that the Town of Lunenberg imposes on subdivisions of more than 25 acres. 
The zoning bylaw at issue (Section 5.6) is designed to encourage developers to preserve open space in developments of more than 25 acres. In return for pursuing a “Cluster Development” (preserving 50% of the site as open space), Section 5.6 reduces the minimum lot size requirement from 40,000 to 30,000 square feet in one district, and from 80,000 to 60,000 square feet in another district. So far so good, but there’s a catch: the bylaw goes on to say that, if the developer decides not to pursue a Cluster Development, the site can only be developed if each lot is at least five acres.
The plaintiff, O’Brien Homes, challenged the validity of this bylaw under M.G.L. c. 240, Section 14A (pdf). It argued that Section 5.6 conflicts with the uniformity requirement of the Zoning Act, unlawfully requires a Cluster Development, and is effectively a taking of land by regulation.
Judge Long rejected these arguments, finding that Section 5.6 applies uniformly to all subdivisions of more than 25 acres within the various zoning districts. He noted that the test for validly distinguishing between larger and smaller subdivisions is whether the distinction has a rational basis and serves a legitimate zoning purpose. Applying that test, Judge Long found that the distinction Section 5.6 is rational and serves two legitimate zoning purposes: preservation of open space and preservation of rural character.
Judge Long observed that clustering is not mandated — it is simply an alternative to five-acre zoning. While acknowledging that the five-acre minimum lot size requirement goes beyond the three-acre requirement that the Supreme Judicial Court carefully scrutinized (before upholding it) in Johnson v. Town of Edgartown (pdf), Judge Long found that Lunenberg’s five-acre provision was not shown to be arbitrary and unreasonable, or unrelated to public health and safety. Finally, Judge Long held that a zoning bylaw that reduces the amount of land that can be developed does not amount to an unconstitutional taking of land.
O’Brien Homes appears to be the first time a Massachusetts court has upheld a minimum lot size requirement greater than three acres. It remains to be seen whether this decision represents the beginning of a trend, or is an anomaly that will remain limited to its particular facts.