Sewage line collapse, county claims my responsibility. How do I find map defining this.

I live right outside of the city limit, literally. I’ve always been told after the ditch was county side and other side being mine. The county also manages “that” side with cutting and digs the ditch out when dirt builds up blocking drainage. (Done on their own, not requested)

How do I find a map with definitive lines as I I recently had a sewage pipe collapse that’s about 15’ on “my” side of the ditch and about 35’ on “their” side of the ditch (including 5’ under the street) but over the phone and without visual reference they let me know “that for sure my side and I’ll need to fix it”

Thanks in advance.