Politically, Obfelden is the youngest municipality in Affoltern, though settlements in the area date back to the Alemannic-Franconian period in the 5th century AD.

Early activity coalesced around five hamlets: Bickwil (first mentioned in 1246 as Bickewilare), Oberlunnern and Unterlunnern (1257 Lundenerun and Lunderun inferioris), Wolsen (1311 Wolunsun), and Toussen (1325 Thunsen).

[3] These five hamlets were known collectively as being ob dem Feld ("over the field") from neighbouring Ottenbach; most fell under the jurisdiction of Maschwanden, although Toussen and part of Unterlunnern came under the Zürich Freiamt.

Both of these areas were merged into Knonau (today's Affoltern district) in the sixteenth century, when the hamlets of Obfelden became a part of the nearby parish of Ottenbach.

The town's coat of arms commemorates this history, with five ears of wheat symbolising the five hamlets, held together by a band representing their union to the new church.