While similar to marriage, a domestic partnership does not necessarily grant the 1,138 rights afforded to married couples in the US by the federal government, as tallied by the United States Government Accountability Office. Furthermore, domestic partnerships are determined by each state or local jurisdiction, so there is no nationwide consistency on the rights, responsibilities and benefits afforded to domestic partners.
Nearly all:
California
Oregon
Nevada
Washington
Some:
Hawaii
Maine
Wisconsin
District of Columbia