resident population
Refers to the number of people who live permanently in a given area, as opposed to transient or daytime population.
The resident population of this town is decreasing year by year.
Compare the number of residents with the number of tourists.
人口 is the general term for 'population', while 定住人口 specifically means 'resident population' as opposed to transient or daytime population.
昼間人口 refers to the daytime population of an area, including commuters and visitors, contrasting with 定住人口 which counts only permanent residents.
Compound of 定住 (ていじゅう, 'settlement, permanent residence') and 人口 (じんこう, 'population').