Do the onxmaps have the names of all private property or is it just listed as private property? Does the onxmaps for an iPhone run off of satellite or cell signal? Or do you just download the map?
OnX list the names of the property owners. On my Android, the app runs off my cell signal. However, if you pre download the map for the area you want, you can go to airplane mode and it will use your phone's GPS to show you where you are. There are several threads on this forum about the app. Their website has a pretty good FAQ section also.

And, I've found several tracts of land previously comsiderd "unhuntable" d/t lack of apparent access. Found a 480acre parcel of property owned by the city and then called the Sheriff, the city and DFW to get the final say so on whether or not the tract is "ok." Yup! They all said to have anyone who takes issue with me hunting it to call them personally. Now, I keep each of their direct lines in my phone in case I need to.
I'm be found state land where I thought it was private. I've found access points into land which I thought was surrounded on all sides by private. I have a hard time scouting now without it. With limited time for boots on the ground scouting OnXMaps has become my best kept "secret."