One of the databases that makes it easy to map your farm or ranch is PLSS. You can read more about it in Wikipedia
A basic building block with which we work is a quarter quarter section (qqsection), which is oftentimes a 40 acre parcel. You can add any of them to your farm definition. For standard qq sections we have an algorithmic approximate generation of quarter quarter quarter quarter sections (q4section), which allows building blocks down to a 2.5 acre parcel.
Our database also contains lots, which are irregular size and shape due to the curvature of the Earth.
In order to use full PLSS functionality and search by township, range and section you will need to log into the system using a Google, Facebook or Twitter account. This will also allow saving of the project so that you can work in stages.