San Mateo is a canton in the Alajuela province of Costa Rica. The head city is in San Mateo district. San Mateo was created on 7 August 186…San Mateo is a canton in the Alajuela province of Costa Rica. The head city is in San Mateo district. San Mateo was created on 7 August 1868 by decree 30. San Mateo has an area of 125.9 km² and a mean elevation of 311 metres.