Absentee voting allows voters who cannot come to polling places a means to cast a ballot. A variety of circumstances, including residency abroad, illness, travel or military service, could prevent voters from coming to the polls on Election Day. Absentee ballots permit registered voters to mail in their votes. The Uniformed and Overseas Citizens Absentee Voting Act, a federal law, governs absentee voting in presidential elections. Absentee voting rules for all other elections are set by the states, and vary. In Oregon, all elections are conducted by mail, but voters have the option of voting in person at county polling stations.

缺席投票为不能够到投票站投票的选民提供了一种投票方法。各种各样的情况（包括居住在国外、疾病、旅行或服兵役）都可能阻止选民在选举日来投票。缺席投票允许登记选民通过邮件投票。《服役及海外公民缺席投票法案》（一个联邦法律）对总统选举的缺席投票进行规范。所有其它选举的缺席投票规则由各州制定，各不相同。在俄勒冈州，所有选举通过邮件进行，但选民可以选择到县投票站亲自投票。