The Victoria County History of Oxfordshire
Two general volumes were published in 1907 and 1939, but detailed work on individual parishes and towns did not begin until the 1950s-60s, with the most recent volume published in August 2019. In all, 19 volumes have been published out of 23 planned, together covering two thirds of the county.
A small team based in Oxford is working to complete the remaining four volumes, of which that on the South Chilterns is well advanced. Work on the other three volumes (to focus on Burford, Chadlington, and Chipping Norton) will begin over the next few years, subject to adequate funding.
Please note that places in the Vale of White Horse (absorbed into Oxfordshire in 1974) were covered in the Berkshire VCH series, published in 1906-27. Current projects all fall within the ancient (pre-1974) county of Oxfordshire.
Eighteen volumes are available on British History Online, though only parts of volumes I and II. For full access to all volumes, check your local library catalogue or your local archive.