I fell down on a cracked sidewalk and Injured seriously. Clearly, the property owner should have maintained the safety of the sidewalk. However, he claims that he didn’t know there was any danger. Can I still hold him responsible?

You need to talk to a lawyer.

Tough case to prove. You might recover enough to pay the lawyer fees.

Where I live, if I want the sidewalk in front of my house repaired, the city and I split the cost of the repair and they handle the logistics.

There is a "reasonable man" concept at play here---and involves some considerations of "assumption of risk" on your part (if applicable) and who is responsible---individually and severally.

Lawyer consultations are usually free.