Unmarried couples remain a relative rarity in Massachusetts, according to the 2000 US Census. Of the 1.33 million households headed by self-described couples, only 130,919 are headed by unmarried partners. Among those living together without benefit of marriage are 7,943 gay male couples and 9,156 lesbian couples.

Not surprisingly, Provincetown is the least matrimonial community in the Bay State, with 90 percent of declared couples living without a license. That rate is bound to decline this summer, assuming gay marriages become legal, since Provincetown is the only locality in the state where most unmarried partners are of same-sex variety. Overall, unmarried-partner households are concentrated in affluent resort areas, sparsely populated communities in the western part of the state, and low-income cities with large nonwhite populations (notably Lawrence, Lowell, and Springfield).

Boston ranks seventh, with 22 percent of its couples unhitched. The inset map, which breaks the city down by US Census tract, shows that unmarried partners are concentrated in the downtown, South End, Jamaica Plain, Roxbury, and Charlestown neighborhoods – and not so much in South Boston, West Roxbury, and parts of Dorchester. (The little square near the center with unusually high marriage rates, by the way, is Chinatown.) Same-sex couples – or at least, same-sex couples willing to tell all to the US Census — account for 21 percent of unmarried households. That translates to 1,951 gay male couples, or one-quarter of all gay male couples in the state. Lesbian couples are less Boston-centric; only 13 percent live in the Hub.

Cities and towns with low numbers of unmarried partners tend to be part of the big “C” around Boston that is also noted for high incomes, high educational levels, and strong support for gay marriage opponent Mitt Romney in the 2002 gubernatorial election. Sherborn is at the bottom of the list, with only 2.2 percent of its couples living outside of wedlock, closely followed by Weston, Westwood, Longmeadow, and Wenham.