Looking at the history of DSN on Wikipedia, it appears that the tens-place digit originally was allocated to identify the region or site, and within a region/site the dishes were numbered sequentially as they came online, but some have been retired while others continued in operation, so the numbering is today a little irregular.
In 1966, Goldstone California had dishes 11, 12, 13, 14; two sites in Australia were 41 and 42; South Africa had 51, Madrid 61, and Canaveral and Ascension (an island in the Atlantic) were 71 and 72.
Over the years the DSN sites were consolidated down to three: Canberra, Madrid, and Goldstone.
When Canberra ran out of numbers in the 40s, apparently they were allocated the 30s as well; likewise Goldstone got the 20s, and Madrid got the rest of the 50s. I think within each decade the antennas are generally numbered more or less sequentially in construction order.