How did Allen County Indiana get this name?

In researching ancestors,Nathaniel Allen and his wife Catherine Rittenhouse, I found (Catherine Rittenhouse, married to Nathan Allen, went into Indiana and lived near Peter, her
brother. Ft Wayne in known as "Allen Country". This was in Catherine's father's (Garrett Rittenhouse's will) I found an Archibald Allen that is most likely Nathaniel's father moved from VA to KY to Indiana and so surmise that Allen County is named after this family.