Markopoulo Mesogaias (Greek: Μαρκόπουλο Μεσογαίας) is a suburban town and a municipality in East Attica, Greece.
The municipality Markopoulo Mesogaias is situated in the Mesogaia plain, in the eastern part of the Attica peninsula, and touches the Aegean Sea coast in the east, where the port town Porto Rafti is located. The town Markopoulo is in the western part of the municipality, at about 80 m elevation. It is 5 km north of Kalyvia Thorikou, 6 km east of Koropi and 21 km southeast of Athens city centre. Greek National Road 89 (Gerakas - Koropi - Lavrio - Sounio) passes through Markopoulo. Athens International Airport is 4 km north of the town. Markopoulo had a railway station on the Athens–Lavrion Railway, which closed for passenger traffic in 1957.
- Agía Triáda (2011 census pop. 218)
- Vravróna, ancient Brauron (pop. 195) - located in the northeast by the Aegean Sea
- Chamoliá (pop. 185)
- Koulidás (pop. 243)
- Markópoulo (pop. 9,513) - the municipal seat
- Poriá (pop. 0)
- Porto Rafti or Limín Markopoúlou (pop. 9,686)
Markopoulo was the home to two venues of the 2004 Summer Olympics: the Markopoulo Olympic Equestrian Centre and the Markopoulo Olympic Shooting Centre.
Markopoulo's women volleyball team plays in the A1 Ethniki Women's Volleyball, the highest level national competition.