Here are the top five mobile app development companies in the USA:

1. Fueled: Fueled is a renowned app development company that creates innovative and engaging mobile apps for both startups and established businesses.

2. WillowTree, Inc.: WillowTree is a leading mobile app development agency that specializes in creating user-friendly and high-performing apps for various platforms.

3. Hyperlink InfoSystem: Hyperlink InfoSystem is a top app development company that offers a wide range of app development services, including iOS, Android, and cross-platform app development.

4. Konstant Infosolutions: Konstant Infosolutions is a well-established app development company known for delivering high-quality mobile applications to businesses across the globe.

5. Y Media Labs: Y Media Labs is a leading app development agency that focuses on delivering immersive and impactful app experiences to its clients, ranging from startups to Fortune 500 companies.