Starbase 123
Starbase 123 was a Federation starbase administered by Starfleet.

In 2366, Starbase 123 detected two Romulan  cruisers on an intercept course with Tin Man, just prior to Starfleet's contact with that lifeform. ()

Appendices

Background information 

According to Star Trek: Star Charts (p. 63) and Stellar Cartography: The Starfleet Reference Library ("Federation Historical Highlights, 2161-2385"), Starbase 123 was located in the Beta Quadrant.

Apocrypha 
This starbase was also referenced in the Pocket TNG  Boogeymen.

External link 
 

bg:Звездна база 123
de:Sternenbasis 123
nl:Sterrenbasis 123
0123, Starbase