=COUNTIFS(Casework!$B:$B,"Disciplinary",Casework!$AB:$AB,">"&EOMONTH(TODAY(),-1))

In implement in Red part of above formula you can change into current month as right now it is -1 in EOMONTH function with today function. Today function will give you current date and EOMONTH function can provide you whatever date you have it will give you that particular month's end date.

EOMONTH(start_date, months)

Start_date Required- A date that represents the starting date. Dates should be entered by using the DATE function, or as results of other formulas or functions. For example, use DATE(2008,5,23) for the 23rd day of May, 2008. Problems can occur if dates are entered as text.

Months Required. The number of months before or after start_date. A positive value for months yields a future date; a negative value yields a past date.

Note- (-1) means before month last date, (+1) next upcoming month last date and 0 means current month last date.

Hope it will help you. If you wish current month then just put 0 instead on (-1)