ZLC controller reported descending in error an aircraft below the mia.

Attributes
ACN	1672463
Time
Date	201908
Local Time Of Day	1801-2400
Place
Locale Reference	GPI.Airport
State Reference	MT
Aircraft 1
Make Model Name	SR22
Operating Under FAR Part	Part 91
Flight Phase	Descent
Flight Plan	IFR
Aircraft 2
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Operating Under FAR Part	Part 91
Person 1
Qualification	Air Traffic Control Fully Certified
Experience	Air Traffic Control Time Certified In Pos 1 (yrs) 9
Events
Anomaly	ATC Issue All Types Deviation - Procedural Clearance Inflight Event / Encounter CFTT / CFIT

Narrative:

Aircraft X was inbound to gpi from the southwest. He was passing through a 9500 ft. Mia (minimum IFR altitude) area. I inadvertently cleared him to 9000 ft. I was on the tail end of a busy session where I had been working multiple gpi approach/departures in addition to activities on the east side of the sector including aircraft Y that needed a reroute and numerous deviations. I did not have a d-side until very shortly before the incident.have more staffing; make mia numbers larger.

Original NASA ASRS Text

Title: ZLC Controller reported descending in error an aircraft below the MIA.

Narrative: Aircraft X was inbound to GPI from the southwest. He was passing through a 9500 ft. MIA (Minimum IFR Altitude) area. I inadvertently cleared him to 9000 ft. I was on the tail end of a busy session where I had been working multiple GPI approach/departures in addition to activities on the east side of the sector including Aircraft Y that needed a reroute and numerous deviations. I did not have a D-side until very shortly before the incident.Have more staffing; make MIA numbers larger.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.