how to find vacant property owners in maryland? Where are the government sites, or others, that are free?

The tax records are your best bet. Every county has their own site and so far as I know they all have the tax records online. I'm assuming you have a property in mind (or several) and want to know who the owner(s) are.

https://sdat.dat.maryland.gov/RealProperty/Pages/d...

Above site is the MD state site you can look up ownership info.

Can I look up owners at the courthouse by street address? I thought you can only look them up by name.

Find the vacant properties and cross reference the addresses at your county court house to look up the tax records. You will find the owner's name and address where the tax bills are sent.

Those sites aren't free and government listings are being viewed by a lot of competition. You would be better off locating a property on your own. The ones that are abandoned are fairly obvious. You take the address and go to that county courthouse to the records department and find who the owners of the property are by locating the deed that is on file. In many cases, the people that own those properties have inherited them and live out of state. At that point, with a little research, you may be able to make an offer directly to them.