halacha - Is a Kohen required to marry a virgin?

In a recent conversation with several friends regarding ba'alei teshuva marrying Kohanim (specifically college students), one person present said that a Kohen can only marry a virgin. I contested this point based on the first Aliyah of Parshat Emor. Plus, I remember at least one explanation that said a regular Kohen can marry a widow, but cannot marry a divorcee. However, that same person says the prohibition for a regular Kohen is derived from the Kohen Gadol.

So, is a regular Kohen allowed to marry a widow or is he - like the Kohen Gadol - required to only marry a virgin?

Answer

From this Chabad article the restrictions on whom a Kohen can marry are:

A kohen may not marry a ge’rusha (divorcee), chalalah (woman of defective kohen status), zonah (woman who previously violated certain sexual prohibitions), giyoret (convert) or chalutzah (a Levirate widow). If he does marry any of them, their children likewise become chalalim. Sons born do not have priestly status, and daughter may not marry kohanim.

The categories are explained in more detail on the site. An ordinary kohen may marry a widow. Only the Kohen Gadol is forbidden to marry a widow because Hashem commanded so in the Torah.

Obviously CYLOR for a real case.

ADDITION For @Zvi, who in the comment below asks for a non-Chabad source, this on Marital defilement is from Wikipedia.

A male Kohen may not marry a divorcee, a prostitute, a convert, or a dishonored woman (חללה) (Leviticus 21:7) A Kohen who enters into such a marriage loses the entitlements of his priestly status while in that marriage. The Kohen is not permitted to forgo his status and marry a woman prohibited to him (Leviticus 21:6-7). However, in the event that a Kohen transgresses a marital restriction, upon termination of the marriage the Kohen is allowed to re-assume his function and duties as a full Kohen.[citation needed]

Modern-day kohanim are also prohibited from marrying a divorcee (even their own divorced wife); a woman who has committed adultery, had been involved in incest, or had relations with a non-Jew; a convert; or the child of two converts. A born-Jewish woman who has had premarital relations may marry a kohen only if all of her partners were Jewish.

This at Jewish Answers.com explains the “zona. prostitute” prohibition;

“Zona” means a prostitute and refers to a Jewish woman who had sex with a non-Jew. A Kohen is designated by G’d to serve Him in a more intimate capacity that other Jews and, as such, he is required to maintain a higher spiritual level. He is not required to marry a virgin but he cannot marry a convert, a divorcee or a prostitute.