Are you the personal representative?

You might want to start by reading IRS Publication 559 (link below).

https://www.irs.gov/publications/p559#en_US_2020_publink100099488

Generally, however, a cash inheritance (or property acquired via operation of law at the death of a co-tenant) is not a taxable event except in certain instances (e.g., a retirement account).

Interest earned on the account will be reported to you by the bank and should be reported on your tax return. 

The account was a joint account with you and your mother.  You should check with the executor of your mother's estate to ensure there are no inheritance tax implications on the funds transferring to you upon her death. 

Tax Implication of Money In Joint Account When One Dies

@mikey500  @tagteam

You would only have to be concerned with inheritance tax in a (very) limited number of states, almost all of them have threshold amounts, and a few exempt transfers to lineal descendants.

The states are: Iowa, Kentucky, Maryland, Nebraska, New Jersey, and Pennsylvania.

@JeffreyR77 @mikey500