My mother recently died. My sister and I are having trouble finding out who the mortgage company is so that we can pay the mortgage. How do you go about finding this info.

You could trace it through her bank. They could locate who the payments were going to. Of course, they would find you fast enough once the payments stopped. Or contact her lawyer, he would have a final accounting with names and addresses.

Check the property taxing authority (county, city, or whatever it is). They often have that sort of information available online.

No statements around the house? No cancelled checks?

As noted
1. look though all of their records
2. they will or should get monthly bills, so check the mail
3.The recorder of Deeds will have the lien on the home filed.
4. It should show up on the tax records

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3.The recorder of Deeds will have the lien on the home filed.
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Yes, the recorder of deeds will have a record of the mortgage. But I believe OP was looking for an easier way. Depending on where this is, researching the deed books can be complicated.