The population of Tatamy was 930 at the 2000 census.
There were 352 households out of which 32.4% had children under the age of 18 living with them, 63.6% were married couples living together, 8.2% had a female householder with no husband present, and 24.1% were non-families. 21.0% of all households were made up of individuals and 10.2% had someone living alone who was 65 years of age or older. The average household size was 2.63 and the average family size was 3.03.
In the borough the population was spread out with 24.8% under the age of 18, 6.0% from 18 to 24, 28.9% from 25 to 44, 28.5% from 45 to 64, and 11.7% who were 65 years of age or older. The median age was 40 years. For every 100 females there were 91.0 males. For every 100 females age 18 and over, there were 89.4 males.
The median income for a household in the borough was $48,942, and the median income for a family was $55,750. Males had a median income of $38,333 versus $26,797 for females. The per capita income for the borough was $21,759. About 2.9% of families and 3.8% of the population were below the poverty line, including 6.2% of those under age 18 and 5.0% of those age 65 or over.