If the arrest was recent
Start with the county jail
Someone just arrested in Maryland is typically held in a COUNTY (or Baltimore City) detention center pending a bail/initial-appearance hearing.
Most detention centers are run by the county; Baltimore City pretrial detention (Central Booking) is run by the state DPSCS.
The most reliable single custody search across Maryland is VINELink/VINE, which in Maryland is managed by DPSCS and is free — it tracks custody status in county jails AND state prisons.
Search by name or offender ID and, if you want, register for free phone/email alerts when custody status changes.
For a very recent booking or bail details, you can also call the county detention center directly.
Detention is mostly county-run in Maryland (Baltimore City pretrial is state-run). Rather than hunt each county roster, use VINELink, the Maryland statewide custody-status system managed by DPSCS that spans county jails and state prisons; call the specific county detention center for a brand-new booking or bail information.