Source: Board of Governors of the Federal Reserve System (US)  

Release: H.4.1 Factors Affecting Reserve Balances (data not included in press release)

Units:  Billions of Dollars, Not Seasonally Adjusted

Frequency:  Monthly

Notes:

Data prior to 1991 are from various issues of Banking and Monetary Statistics and the Annual Statistical Digest. Data from 1991 forward are calculated using data from the H.4.1 Release - Factors Affecting Reserve Balances.
As of March 1, 2019, this series is calculated as a monthly average of fred.stlouisfed.org/series/WCURCIR.

Source: Federal Reserve Bank of St. Louis  

Release: St. Louis Monthly Reserves and Monetary Base  

Units:  Billions of Dollars, Seasonally Adjusted

Frequency:  Monthly

Notes:

Updates of this series will be ceased on December 20, 2019. There is no replacement to this seasonally adjusted series. Interested users can construct a proxy of not seasonally adjusted data as the difference between monetary base from the H.3 release and currency component of M1 from the H.6 release. The discontinued series plotted on the same graph with the calculated data can be accessed for comparison here.
For more details, see the FRED Announcement.