Can a Non-Virgin Woman Marry a Cohen?

Greetings, 

A woman who has had relations with a non-Jew is forbidden to marry a Cohen; however, a woman who has had relations with a Jew (for whom there is no biblical prohibition or positive commandment against marrying, and who is not forbidden to her due to ervah) is permitted to marry a Cohen, even though she is not a virgin. 

Sources: Shulchan Aruch Even HaEzer (Siman 6, Se'if 8). It is noted there (Se'if 17) that if a single woman is seen to have been with a man, and the man leaves, and they ask her who it was and she says a respectable man, she is considered trustworthy. Moreover, even if she is pregnant and says from whom, and states a respectable man, she too (and her daughter) is permitted to a Cohen. This applies in cases where the location where she was with the man is a crossroads or fields where many passersby are respectable, and most of the inhabitants are known to be respectable such that the Sages required two majorities. But if most passersby disqualify her, such as non-Jews or mamzerim, even if the majority of the area is respectable, or most people from the city are disqualified, though the majority of passersby are respectable, they are concerned and say she was with one who disqualifies her, and she may not marry a Cohen initially; if she does marry, the marriage does not take effect. In any case, where two majorities are required to permit her to a Cohen, this is when we know she has indeed been with someone even without her admission. But when we know only from her statement that she has been with someone, the ruling is that she is believed to have been with a Jew and not a non-Jew even without the two majorities. See responsa Tshuvot VeHanhagot parts 1 (Siman 76), 3 (Siman 99), 4 (Siman 240), and 6 (Siman 256). 

Wishing you much success, Hillel Meirs