Is this crack in block foundation/under pinning something to worry about
That looks like settlement cracks.  
Whether you should worry about it depends on several things: 


what is that supporting?  
Is it still settling?  



This is 100 yr old construction, so there will have been settlement.  The question is whether that settlement is done or you have a new problem.  Water can be a source of new settlement, and it can become a new problem on old construction.  

The pictures look like there is a water problem in that area so even if it isn't causing settlement issues, it will create a mold problem.  Look for easy to spot, easy to fix water issues (gutters that need cleaning, gutters that have pulled away from the house, clogged downspouts, downspouts discharging near the house, poor grading around the foundation, etc.).

That corner is supporting something.  A typical first step is to stick an indicator on the crack.  You can get simple measuring tools like this that just lets you measure and record the size of the crack: https://www.amazon.com/CRACKMON-224R-Comparator-224R-01-Compliant/dp/B00K5HXJB0

A more reliable indicator is a simple gauge that is glued across the crack and shows the current alignment.  For example:  https://www.amazon.com/CRACKMON%C2%AE-4020A-Heavy-Duty-Building-Foundation/dp/B00QWFYA7G
You leave it in place and check it every few weeks.  If there is any additional movement, it is easy to see.  You could just watch it.  If there is no movement in say half a year, that indicates that it's old settlement and you don't need to worry about it. 

Another possibility: if there are existing piers, this may be a problem that has already been fixed. 

If you do see new movement, it would be important to take remedial steps.  I would have a foundation repair specialist evaluate it (often no charge for an initial look and recommendations on how to proceed).