Russians in Georgia 

First, here's some statistics (all the Soviet censuses) for Georgia proper, South Ossetia and Abkhazia. It's in Russian but you shouldn't have any difficulties with these tables (Russians are "русские" in Russian, just find appropriate columns).

Georgia

Ethnic Russians appeared in Georgia in significant numbers after Georgia became part of the Russian Empire in 1803 (Kartli and Kakheti) - 1878 (Ajara). There were 79082 and 19273 people who indicated Russian as their mother language in Tiflis Governorate  and Kutais Governorate  respectively. Dukhobors have to be mentioned as well.

As you can see from the census data the Russian population had risen from 83 to the maximum of 319 thousand between 1926 and 1959 and then began to decline slowly to 266 thousand in 1989. Migration and lower birth rates were the main reasons of this decline.

Obviously, many Russians left Georgia during the 1990s due to economic hardships (mainly, imho) and other reasons.

Abkhazia
...