It is a part of the municipality of Stichtse Vecht, and lies about 13 km northeast of Woerden.

The hamlet was first mentioned in 1138 as "juxta lacum qui vocatur A" (translation: Next to the lake called A), and refers to the Aa River which is a tributary of the Angstel River.

Oud (old) has been added to distinguish from Nieuwer-Ter-Aa.

The castle Ruwiel was located in Oud-Aa, however it was destroyed in 1673 by the French, and now contains a farm.

This Utrecht location article is a stub.